The existing logic for killing pub-sub clients did not handle the `allchannels`
permission correctly. For example, if you:
ACL SETUSER foo allchannels
Have a client authenticate as the user `foo` and subscribe to a channel, and then:
ACL SETUSER foo resetchannels
The subscribed client would not be disconnected, though new clients under that user
would be blocked from subscribing to any channels.
This was caused by an incomplete optimization in `ACLKillPubsubClientsIfNeeded`
checking whether the new channel permissions were a strict superset of the old ones.
f38aa6bfb7