public void cancelSubscription(NodeSubscription subscription) {
        cancelSubscription(subscription, ClusterManager.isClusteringEnabled());
    }
Cancels an existing subscription to the node. If the subscriber does not have any
other subscription to the node and his affiliation was of type {@code none} then
remove the existing affiliation too.

@param subscription the subscription to cancel.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/Node.java