Profile page: enable comment editing

Giving users the ability to edit their own comments from their user page is
something that RES adds, but we didn't because the data wasn't available or
something.  Someone [brought it up again][0] recently, and it turns out it
*just works* now if we enable it.  And I don't see a good reason to prevent
users from doing it.

[0]: https://www.reddit.com/r/AutoModerator/comments/2olykv/automoderators_flair_and_karma_have_been_wiped/cmoiz4j?context=1