Remove the FAQ and redirect to ecosystem-wide FAQ

[Yoshanuikabundi]

See openforcefield/openff-docs#63, #1932. Closes #1848.

This doesn't add a redirect from the current FAQ URL to the new one - I'll add that by hand in RTD when I merge this.

• Update changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.76%. Comparing base (c84b321) to head (b14b606).

Additional details and impacted files

[j-wags]

I'm seeing one more link that needs to be updated in the logs -
generating indices... /home/docs/checkouts/readthedocs.org/user_builds/open-forcefield-toolkit/checkouts/1934/docs/users/molecule_cookbook.ipynb:130002: WARNING: 'myst' cross-reference target not found: '../faq.md#im-getting-stereochemistry-errors-when-loading-a-molecule-from-a-smiles-string' [myst.xref_missing]