Delete unused languages_users table from db

[FireLemons]

What changed, and why?

Deleted languages_users table from db because I suspect user_languages is used instead.

How is this tested? (please write tests!) 💖💪

Adding a language to a user only makes a row in the latter table

Do not merge until we can confirm the prod version of languages_users has no rows

[FireLemons]

The prod data says the languages_users table does have rows but the user_languages contains all the rows the languages_users table has with additional rows from later in time.

See: 43bc4e9

I think it's safe to drop the unused table