When a server leaves a room it may stop sharing a room with remote
users, and thus not get any updates to their device lists. So we need to
check for this case and mark those device lists and stale.

We don't need to do this if we stop sharing a room because the remote
user leaves the room, because we track that case via looking at
membership changes.

Co-Authored-By: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

…rk_left_rooms_as_stale