UNSUBSCRIBE [channel [channel ...]]
Time complexity: O(N) where N is the number of clients already subscribed to a channel.
Unsubscribes the client from the given channels, or from all of them if none is given.
When no channels are specified, the client is unsubscribed from all the previously subscribed channels. In this case, a message for every unsubscribed channel will be sent to the client.
user:1> SUBSCRIBE foo bar quax
dragonfly> PUBLISH foo message
dragonfly> PUBLISH bar message
recieved 'message' in foor
recieved 'message' in bar
<user:1 will not recieve any more messages>