Doc simplify footer
[x] closes #51536 - Simplified pandas theme footer by removing custom template dependency
[x] Tests added and passed - Documentation changes don't require additional tests, but the build process validates the changes
[x] All code checks passed - Changes follow pandas documentation standards and use proper reStructuredText formatting
[x] Added type annotations - Not applicable for documentation-only changes
[x] Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file - Entry already exists in doc/source/whatsnew/v3.0.0.rst under "Documentation changes" section
Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.