PERF: Revert all inboxes from messages route. (PR #14445)

The all inboxes was introduced in 016efeadf6f242e04daf5ef8e18c2ca708a1392d but we decided to roll it back for performance reasons. The main performance challenge here is that PG has to basically loop through all the PMs that a user is allowed to view before being able to order by Topic#bumped_at. The all inboxes was not planned as part of the new/unread filter so we’ve decided not to tackle the performance issue for the upcoming release.

Follow-up to 016efeadf6f242e04daf5ef8e18c2ca708a1392d


Thank you @lis2