User search: Remove trigram and refactor the module
- Remove trigram as it tends to rank garbage results highly, resulting in it prioritized above fts, which gives actually decent results. ACKed by kaniini and lain on irc.
- Remove a test for handling misspelled requests, since we no longer have trigram
- Remove a test for searching users with
nil
display names, because it is unrealistic, we don't accept usernames that are not >1 char strings - Make rank boosting for followers/followees sane again, previous values resulted in garbage matches getting on top just because the users are followers/followees