Revert "Special-handle Empathy to have multiple sources and to queue notifications"

This reverts commit bb0a977edc.

https://bugzilla.gnome.org/show_bug.cgi?id=608999

js/ui/messageTray.js

@@ -329,7 +329,6 @@ Source.prototype = {
         this.text = null;
         if (createIcon)
             this.createIcon = createIcon;
-        this.handleReplacing = true;
     },
 
     // This can be overridden by a subclass, or by the createIcon
@@ -565,7 +564,7 @@ MessageTray.prototype = {
     },
 
     _onNotify: function(source, notification) {
-        if (!notification.source.handleReplacing || this._getNotification(notification.id, source) == null) {
+        if (this._getNotification(notification.id, source) == null) {
             notification.connect('destroy',
                                  Lang.bind(this, this.removeNotification));
             this._notificationQueue.push(notification);