* Reset status cache when status_stat or media_attachment updates
Fix#8711
Media attachments are generally immutable, but admins can update
the sensitive flag, and this would ensure the change is visible
instantly. Same for updates to status stats. That is a regression
from #8185, because even the correct updated_at fetched from a join
doesn't seem to invalidate the cache.
* Remove join from Status#cache_ids since it has no effect
Claire