An announcement room the user is not a member of is now listed when it
holds an announcement, or when the user left, was kicked or was banned
within the request's window, and otherwise left out. A user removed
before anything was announced no longer gets the room on a new
connection, and a user leaving on their own before any announcement gets
the synthetic join in the same response instead of their leave.
The room is then never sent with the user's real leave, so resending it
from scratch afterwards is no longer needed.