#1588 Send a presence unsubscribe to all contacts when removing a user
Description of feature:
When a user gets removed, whether of their own volition or through some admin feature, send a presence unsubscribe and unsubscribed to all of their contacts.
This tries to keep other users’ rosters from growing with now-inexistent contacts. Also useful when spammers get caught, to clean their victims’ roster (and hopefully cancel any query they might have sent in bulk).