docs: removes databases package recommendation

[AllenSH12]

Summary

Starts on closing out https://github.com/encode/starlette/issues/1921

TODOs:

• [ ] Propose updated query/transaction sections

Checklist

• [x] I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• [ ] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.