Remove deprecated headers (#2939)

Depends on rapidsai/cuvs#1763. Resolves #2937

This PR does the following:
1. Removes files with the following message
```cpp
#ifndef RAFT_HIDE_DEPRECATION_WARNINGS
#pragma message(__FILE__                                                  \
                " is deprecated and will be removed in a future release." \
                " Please use the raft/sparse/solver version instead.")
#endif
```
2. Removes files with the following message
```cpp
/**
 * This file is deprecated and will be removed in a future release.
 */
```
3. Pulls from correct non-deprecated headers like using`raft/util/cudart_utils.cuh` instead of `raft/core/cudart_utils.cuh`
4. Pulls correct functionality from non-deprecated headers like using `raft/linalg/matrix_vector.cuh` instead of `raft/matrix/math.cuh`. This requires using the newer mdspan based apis.
5. Consolidates `gemm.cuh` and `gemm.hpp` into just `gemm.cuh`

**Update:**
There were a couple of fixes included in this PR that I have decoupled. Instead those fixes should be merged in #2940.
This will allow us to unravel the merging sequence better to avoid breaking changes altogether. Still marking this PR as breaking for awareness purposes.
After merging #2940, the cuml side and cuvs side can be updated to use the non-deprecated apis. Then we can merge this raft PR to remove the deprecated and unused headers.

**Update:**
There are a couple of breaking changes that affect cugraph and cuopt, so we will need to merge fixes for those first.

**Merging sequence:**
#2940 -> rapidsai/cuvs#1763 -> rapidsai/cuml#7752 -> rapidsai/cuml#7797 -> rapidsai/cugraph#5429 -> NVIDIA/cuopt#865 -> #2939

**Downstream libraries CI status:**
cuvs: 🟢
cuml: 🟢
cugraph: 🟢
cuopt: 🟢

Authors:
  - Anupam (https://github.com/aamijar)

Approvers:
  - Bradley Dice (https://github.com/bdice)
  - Divye Gala (https://github.com/divyegala)
  - Dante Gama Dessavre (https://github.com/dantegd)

URL: #2939

Author: aamijar

cpp/CMakeLists.txt

@@ -450,13 +450,6 @@ install(
   DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
 )
 
-# Temporary install of raft.hpp while the file is removed
-install(
-  FILES include/raft.hpp
-  COMPONENT raft
-  DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/raft
-)
-
 install(
   FILES ${CMAKE_CURRENT_BINARY_DIR}/include/raft/version_config.hpp
   COMPONENT raft

cpp/bench/prims/core/copy.cu

@@ -1,16 +1,16 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 #include <common/benchmark.hpp>
 
 #include <raft/core/copy.cuh>
-#include <raft/core/cudart_utils.hpp>
 #include <raft/core/device_mdarray.hpp>
 #include <raft/core/device_resources.hpp>
 #include <raft/core/host_mdarray.hpp>
 #include <raft/core/mdspan_types.hpp>
 #include <raft/core/memory_type.hpp>
+#include <raft/util/cudart_utils.hpp>
 
 #include <cuda/std/mdspan>
 

cpp/include/raft.hpp

@@ -1,12 +1,12 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2021-2024, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2021-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 
 #pragma once
 
-#include <raft/comms/comms.hpp>
 #include <raft/comms/detail/test.hpp>
+#include <raft/core/comms.hpp>
 #include <raft/core/resources.hpp>
 
 namespace raft {