Clean up Sphinx configuration and remove redundant code

[dhruvatr]

Description

Checklist

• PR is against master (or maintenance branch if only applicable there)
• New code has tests and docs where appropriate
• Tests pass (run tox or the relevant test subset)
• Commit messages are clean and reference related issues

Summary

This PR performs minor cleanup in the Sphinx configuration file:

• Removed redundant app.setup_extension("sphinxcontrib.jquery") call.
• Removed the unused initial extensions = [] assignment.
• Reformatted html_sidebars for better readability.
• Reformatted extlinks dictionary for consistency.

Type of Change

• Documentation
• Code cleanup
• No functional changes

Testing

• No functional changes were made.
• Configuration remains valid.

[ThomasWaldmann]

did you check whether we use jquery somewhere?

[ThomasWaldmann]

@dhruvatr we use a specific black version (see requirements.d/*) to auto-format our stuff.