Remove `language_overrides` setting alias (#13164)

This PR removes the `language_overrides` alias for the `languages`
setting.

I've seen a number of people run into issues where they have both
`languages` and `language_overrides` in their settings and get confused
when their settings don't seem to apply as expected.

This is a breaking change, but I think it is a necessary one to prevent
more users from running into issues.

Release Notes:

- Breaking Change: Removed the `language_overrides` alias for the
`languages` setting. If you have settings under `language_overrides`
they should get moved to `languages`.