Investigate if we can drop `index_users_on_accepted_term_id`

Preliminary Investigation

1. This index doesn't seem to have had any scans, ever
2. An 'accepted term' is an ApplicationSetting::Term which has a belongs_to relationship with User.
3. This index might be useful to find a user associated with a given accepted term id, but checking the code I specified above as well as the User model, I don't find any instance in which this index would be useful.

I recommend dropping it.