Restore matplotlib.__doc__ in Sphinx docs

[QuLogic]

PR Summary

Since we already have an explicit listing of module members, that needs to be turned off here. Also, don't add it to the index as we already have matplotlib pointing to the top level page (though maybe that should change?)

Fixes #17973

PR Checklist

Tests and Styling

• [n/a] Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• [n/a] New features are documented, with examples if plot related.
• [n/a] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [n/a] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).

[tacaswell]

Looks good except the last module entry renders differently

I'm going to push another commit to this to fix this is a different way.