void childNodeDeleted(Node child) {
        // Build packet to broadcast to subscribers
        Message message = new Message();
        Element event = message.addChildElement("event", "http://jabber.org/protocol/pubsub#event");
        event.addElement("delete").addAttribute("node", child.getUniqueIdentifier().getNodeId());
        Log.trace("Broadcast event notification to subscribers that child ('{}') was deleted.", child.getNodeID());
        broadcastCollectionNodeEvent(child, message);
    }
Notification that a child node was deleted from this node. Trigger notifications
to node subscribers whose subscription type is {@link NodeSubscription.Type#nodes} and
have the proper depth.

@param child the deleted node that was removed from this node.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/CollectionNode.java