[CI/dep] Update docsy + submodule workaround

[chalin]

• Contributes to Docsy breaking change: adjust for new path_base_for_github_subdir  #3922
• Bring in new version of Docsy with the breaking change. For details, see https://github.com/google/docsy/blob/main/CHANGELOG.md
• Deletes temporary layouts/partials/page-meta-links.html
• Tweaks scripts/content-modules/adjust-pages.pl so that we don't have to wait for submodules to be update before the Docsy update can be used

No effective change in generated site files, which in particular means that Repository Links are being generated the same as before:

$ (cd public && git diff -bw --ignore-blank-lines) | grep ^diff
diff --git a/site/index.html b/site/index.html