sagemathgh-41077: Cleanup gitignore file
    
Now that we use meson with a full out-of-tree build, we no longer need
to gitignore generated files in the src folder. In fact, it's strongly
recommended that those older files should be deleted so that they don't
get accidentally picked-up by Python at runtime.

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<!-- ^ Don't put issue numbers in the title, do this in the PR
description below. -->
<!-- ^ For example, instead of "Fixes sagemath#12345" use "Introduce new method
to calculate 1 + 2". -->
<!-- v Describe your changes below in detail. -->
<!-- v Why is this change required? What problem does it solve? -->
<!-- v If this PR resolves an open issue, please link to it here. For
example, "Fixes sagemath#12345". -->



### 📝 Checklist

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- [ ] The title is concise and informative.
- [ ] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
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URL: sagemath#41077
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik, Tobias Diez

Author: Release Manager

.gitignore

@@ -25,34 +25,9 @@
 /m4/sage_spkg_configures.m4
 /m4/sage_spkg_versions*.m4
 
-# no longer generated, but may still be in user worktrees
-/src/lib/pkgconfig
-
 # Conda environment files (auto-generated)
 /environment-3.[0-9].yml
 /environment-3.[0-9][0-9].yml
-# The following files are no longer generated but may still be in users' directories
-/environment.yml
-/environment-dev-3.9.yml
-/environment-dev-3.10.yml
-/environment-dev-3.11.yml
-/environment-optional.yml
-/environment-optional-3.9.yml
-/environment-optional-3.10.yml
-/environment-optional-3.11.yml
-/src/environment.yml
-/src/environment-3.9.yml
-/src/environment-3.10.yml
-/src/environment-3.11.yml
-/src/environment-dev.yml
-/src/environment-dev-3.9.yml
-/src/environment-dev-3.10.yml
-/src/environment-dev-3.11.yml
-/src/environment-optional.yml
-/src/environment-optional-3.9.yml
-/src/environment-optional-3.10.yml
-/src/environment-optional-3.11.yml
-
 
 # Various editors
 *~
@@ -140,45 +115,6 @@ __pycache__/
 **/*.py[cod]
 *$py.class
 
-# Generated by sage_setup.autogen
-/src/sage/ext/interpreters
-!/src/sage/ext/interpreters/meson.build
-!/src/sage/ext/interpreters/README
-
-# Generated Cython files
-*.so
-**/*.so
-**/*.so.old
-/src/cython_debug
-# Most C and C++ files are generated by Cython and should not
-# be included in the sdist.
-/src/sage/**/*.c
-/src/sage/**/*.cpp
-# C header generated by Cython
-/src/sage/modular/arithgroup/farey_symbol.h
-# List of C and C++ files that are actual source files,
-# NOT generated by Cython
-!/src/sage/graphs/base/boost_interface.cpp
-!/src/sage/graphs/cliquer/cl.c
-!/src/sage/graphs/graph_decompositions/sage_tdlib.cpp
-!/src/sage/libs/eclib/wrap.cpp
-!/src/sage/libs/linkages/padics/relaxed/flint_helper.c
-!/src/sage/misc/inherit_comparison_impl.c
-!/src/sage/modular/arithgroup/farey.cpp
-!/src/sage/modular/arithgroup/sl2z.cpp
-!/src/sage/rings/bernmm/bern_modp.cpp
-!/src/sage/rings/bernmm/bern_modp_util.cpp
-!/src/sage/rings/bernmm/bern_rat.cpp
-!/src/sage/rings/bernmm/bernmm-test.cpp
-!/src/sage/rings/padics/transcendental.c
-!/src/sage/rings/polynomial/weil/power_sums.c
-!/src/sage/schemes/hyperelliptic_curves/hypellfrob/hypellfrob.cpp
-!/src/sage/schemes/hyperelliptic_curves/hypellfrob/recurrences_ntl.cpp
-!/src/sage/stats/distributions/dgs_bern.c
-!/src/sage/stats/distributions/dgs_gauss_dp.c
-!/src/sage/stats/distributions/dgs_gauss_mp.c
-!/src/sage/symbolic/ginac/*.cpp
-
 # Temporary build files
 build/temp.*/
 build/bin/sage-build-env-config
@@ -244,16 +180,6 @@ build/pkgs/wheel/version_requirements.txt
 /build/pkgs/*/src/*.egg-info
 /build/pkgs/*/src/.tox
 
-# Generated by docbuild
-/src/doc/en/reference/*/sage
-/src/doc/en/reference/*/sage_docbuild
-/src/doc/en/reference/sage
-/src/doc/en/reference/spkg/*.rst
-!/src/doc/en/reference/spkg/index.rst
-/src/doc/output
-/src/doc/en/installation/*.txt
-/src/doc/en/reference/repl/*.txt
-
 # Distribution / packaging
 src/*.egg-info/
 /src/.cython_version
@@ -288,12 +214,6 @@ src/.coverage/
 worktree*
 **/worktree*
 
-# Meson build directory
-builddir
-builddir-*
-build-install
-build/cp*
-
 # Meson subprojects
 /subprojects/*
 !/subprojects/*.wrap
@@ -313,6 +233,7 @@ src/sage/dynamics/cellular_automata/__init__.py
 src/sage/dynamics/arithmetic_dynamics/__init__.py
 src/sage/dynamics/__init__.py
 src/sage/dynamics/complex_dynamics/__init__.py
+src/sage/ext/interpreters/__init__.py
 src/sage/knots/__init__.py
 src/sage/topology/__init__.py
 src/sage/functions/__init__.py
@@ -470,3 +391,8 @@ src/sage/calculus/__init__.py
 # ci-meson.yml runs a `./tools/test-git-no-uncommitted-changes` step)
 /.ccache
 /setup-miniconda-patched-environment-*.yml
+
+# bootstrap-time generated docs
+/src/doc/en/installation/*.txt
+/src/doc/en/reference/spkg/*.rst
+!/src/doc/en/reference/spkg/index.rst