Drop pkg_resources from stubinfo

[hauntsaninja]

Fixes #18839

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pwndbg (https://github.com/pwndbg/pwndbg)
+ pwndbg/exception.py:51: error: Cannot find implementation or library stub for module named "pkg_resources"  [import-not-found]
- pwndbg/exception.py:51: error: Library stubs not installed for "pkg_resources"  [import-untyped]
- pwndbg/exception.py:51: note: Hint: "python3 -m pip install types-setuptools"

scipy (https://github.com/scipy/scipy)
+ scipy/_build_utils/tempita/_tempita.py:1041: error: Cannot find implementation or library stub for module named "pkg_resources"  [import-not-found]
- scipy/_build_utils/tempita/_tempita.py:1041: error: Library stubs not installed for "pkg_resources"  [import-untyped]
- scipy/_build_utils/tempita/_tempita.py:1041: note: Hint: "python3 -m pip install types-setuptools"
- scipy/_build_utils/tempita/_tempita.py:1041: note: (or run "mypy --install-types" to install all missing stub packages)
- scipy/_lib/unuran/get_and_clean_unuran.py:8: error: Library stubs not installed for "pkg_resources"  [import-untyped]
+ scipy/_lib/unuran/get_and_clean_unuran.py:8: error: Cannot find implementation or library stub for module named "pkg_resources"  [import-not-found]