Remove all infrastructure around approving or rejecting user name
changes. Name changes haven't been moderated for several years.
* Remove status, approver_id, change_reason, and rejection_reason fields.
* Remove approve and reject controller actions.
Fineprint text was variously styled with `.info`, `.tn`, `.hint`, or
`.cost-footnote` css classes. Standardize on `.fineprint` instead. Use
`.hint` only for form hints and `.tn` only for <tn> tags in translation
notes.
Incidentally changes the font size of form hints to 0.8em (was 0.7em)
and the color of fineprint to #888 (was #AAA or #666).
