Remove conditional compilation blocks leftover from cuml-cpu (rapidsai#6572)

We're no longer releasing builds of `cuml-cpu`. This PR:

- Removes the previous `IF GPUBUILD` blocks used to conditionally guard compilation for `cuml-cpu` builds. I didn't remove or simplify the usage of `gpu_only_import`/`cpu_only_import`, this PR is only tackling removal of the conditional compilation.
- Removes setting `GPUBUILD` in the cmake file
- Since the latter effectively breaks `cuml-cpu` builds, I went ahead and fully removed `cuml-cpu` from our cmake setup.

Fixes rapidsai#6231. Part of rapidsai#6523.

Authors:
  - Jim Crist-Harif (https://github.com/jcrist)

Approvers:
  - Gil Forsyth (https://github.com/gforsyth)
  - Bradley Dice (https://github.com/bdice)
  - Simon Adorf (https://github.com/csadorf)

URL: rapidsai#6572

Author: jcrist

build.sh

@@ -18,7 +18,7 @@ ARGS=$*
 # script, and that this script resides in the repo dir!
 REPODIR=$(cd "$(dirname $0)"; pwd)
 
-VALIDTARGETS="clean libcuml cuml cuml-cpu cpp-mgtests prims bench prims-bench cppdocs pydocs"
+VALIDTARGETS="clean libcuml cuml cpp-mgtests prims bench prims-bench cppdocs pydocs"
 VALIDFLAGS="-v -g -n --allgpuarch --singlegpu --nolibcumltest --nvtx --show_depr_warn --codecov --ccache --configure-only -h --help "
 VALIDARGS="${VALIDTARGETS} ${VALIDFLAGS}"
 HELP="$0 [<target> ...] [<flag> ...]
@@ -27,7 +27,6 @@ HELP="$0 [<target> ...] [<flag> ...]
    libcuml           - build the cuml C++ code only. Also builds the C-wrapper library
                        around the C++ code.
    cuml              - build the cuml Python package
-   cuml-cpu          - build the cuml CPU Python package
    cpp-mgtests       - build libcuml mnmg tests. Builds MPI communicator, adding MPI as dependency.
    prims             - build the ml-prims tests
    bench             - build the libcuml C++ benchmark
@@ -306,8 +305,3 @@ if (! hasArg --configure-only) && (completeBuild || hasArg cuml || hasArg pydocs
         make html
     fi
 fi
-
-if hasArg cuml-cpu; then
-    SKBUILD_CMAKE_ARGS="-DCUML_CPU=ON;-DCMAKE_MESSAGE_LOG_LEVEL=VERBOSE" \
-        python -m pip install --no-build-isolation --no-deps --config-settings rapidsai.disable-cuda=true ${REPODIR}/python/cuml
-fi

python/cuml/CMakeLists.txt

@@ -16,16 +16,11 @@ cmake_minimum_required(VERSION 3.30.4 FATAL_ERROR)
 
 include(../../cmake/rapids_config.cmake)
 
-option(CUML_CPU "Build only cuML CPU Python components." OFF)
 set(language_list "CXX")
 
-if(NOT CUML_CPU)
-  # We always need CUDA for cuML GPU because the raft dependency brings in a
-  # header-only cuco dependency that enables CUDA unconditionally.
-  include(rapids-cuda)
-  rapids_cuda_init_architectures(cuml-python)
-  list(APPEND language_list "CUDA")
-endif()
+include(rapids-cuda)
+rapids_cuda_init_architectures(cuml-python)
+list(APPEND language_list "CUDA")
 
 project(
   cuml-python
@@ -41,7 +36,6 @@ option(USE_LIBCUML_WHEEL "Use libcuml wheel to provide some dependencies" OFF)
 
 # todo: use CMAKE_MESSAGE_CONTEXT for prefix for logging.
 # https://github.com/rapidsai/cuml/issues/4843
-message(VERBOSE "CUML_PY: Build only cuML CPU Python components.: ${CUML_CPU}")
 message(VERBOSE "CUML_PY: Disabling all mnmg components and comms libraries: ${SINGLEGPU}")
 
 set(CUML_ALGORITHMS "ALL" CACHE STRING "Choose which algorithms are built cuML. Can specify individual algorithms or groups in a semicolon-separated list.")
@@ -52,70 +46,39 @@ set(CUML_CPP_SRC "../../cpp")
 ################################################################################
 # - Process User Options  ------------------------------------------------------
 
-if(CUML_CPU)
-  set(CUML_UNIVERSAL OFF)
-  set(SINGLEGPU ON)
-
-  # only a subset of algorithms are supported in CPU-only cuML
-  set(CUML_ALGORITHMS "linearregression")
-  list(APPEND CUML_ALGORITHMS "pca")
-  list(APPEND CUML_ALGORITHMS "tsvd")
-  list(APPEND CUML_ALGORITHMS "elasticnet")
-  list(APPEND CUML_ALGORITHMS "logisticregression")
-  list(APPEND CUML_ALGORITHMS "ridge")
-  list(APPEND CUML_ALGORITHMS "lasso")
-  list(APPEND CUML_ALGORITHMS "umap")
-  list(APPEND CUML_ALGORITHMS "knn")
-  list(APPEND CUML_ALGORITHMS "hdbscan")
-  list(APPEND CUML_ALGORITHMS "dbscan")
-  list(APPEND CUML_ALGORITHMS "kmeans")
-
-  # this won't be needed when we add CPU libcuml++ (FIL)
-  set(cuml_sg_libraries "")
-
-  list(APPEND CYTHON_FLAGS
-  "--compile-time-env GPUBUILD=0")
-
-# cuml-cpu does not need libcuml++.so
-else()
-
-  include(rapids-cpm)
-  include(rapids-export)
-  rapids_cpm_init()
-
-  # --- treelite --- #
-  # Need to call get_treelite explicitly because we need the correct
-  # ${TREELITE_LIBS} definition for RF.
-  #
-  # And because cuml Cython code needs the headers to satisfy calls like
-  # 'cdef extern from "treelite/c_api.h"'
-
-  # wheel builds use a static treelite, because the 'libtreelite.so' in 'treelite' wheels
-  # isn't intended for dynamic linking by third-party projects (e.g. hides its symbols)
-  if(USE_LIBCUML_WHEEL)
-    set(CUML_PYTHON_TREELITE_TARGET treelite::treelite_static)
-    set(CUML_USE_TREELITE_STATIC ON)
-  else()
-    set(CUML_PYTHON_TREELITE_TARGET treelite::treelite)
-    set(CUML_USE_TREELITE_STATIC OFF)
-  endif()
+include(rapids-cpm)
+include(rapids-export)
+rapids_cpm_init()
 
-  set(CUML_EXCLUDE_TREELITE_FROM_ALL ON)
+# --- treelite --- #
+# Need to call get_treelite explicitly because we need the correct
+# ${TREELITE_LIBS} definition for RF.
+#
+# And because cuml Cython code needs the headers to satisfy calls like
+# 'cdef extern from "treelite/c_api.h"'
+
+# wheel builds use a static treelite, because the 'libtreelite.so' in 'treelite' wheels
+# isn't intended for dynamic linking by third-party projects (e.g. hides its symbols)
+if(USE_LIBCUML_WHEEL)
+set(CUML_PYTHON_TREELITE_TARGET treelite::treelite_static)
+set(CUML_USE_TREELITE_STATIC ON)
+else()
+set(CUML_PYTHON_TREELITE_TARGET treelite::treelite)
+set(CUML_USE_TREELITE_STATIC OFF)
+endif()
 
-  include(${CUML_CPP_SRC}/cmake/thirdparty/get_treelite.cmake)
+set(CUML_EXCLUDE_TREELITE_FROM_ALL ON)
 
-  # --- libcuml --- #
-  find_package(cuml "${RAPIDS_VERSION}" REQUIRED)
+include(${CUML_CPP_SRC}/cmake/thirdparty/get_treelite.cmake)
 
-  set(cuml_sg_libraries cuml::${CUML_CPP_TARGET})
-  set(cuml_mg_libraries cuml::${CUML_CPP_TARGET})
+# --- libcuml --- #
+find_package(cuml "${RAPIDS_VERSION}" REQUIRED)
 
-  if(NOT SINGLEGPU)
-    list(APPEND cuml_mg_libraries cumlprims_mg::cumlprims_mg)
-  endif()
+set(cuml_sg_libraries cuml::${CUML_CPP_TARGET})
+set(cuml_mg_libraries cuml::${CUML_CPP_TARGET})
 
-  list(APPEND CYTHON_FLAGS
-  "--compile-time-env GPUBUILD=1")
+if(NOT SINGLEGPU)
+list(APPEND cuml_mg_libraries cumlprims_mg::cumlprims_mg)
 endif()
 
  ################################################################################
@@ -124,12 +87,6 @@ endif()
 include("${CUML_CPP_SRC}/cmake/modules/ConfigureAlgorithms.cmake")
 include(cmake/ConfigureCythonAlgorithms.cmake)
 
-if(CUML_CPU)
-  # libcuml requires metrics built if HDSCAN is built, which is not the case
-  # for cuml-cpu
-  unset(metrics_algo)
-endif()
-
 message(VERBOSE "CUML_PY: Building cuML with algorithms: '${CUML_ALGORITHMS}'.")
 
 include(rapids-cython-core)