messageTray: Do not show the summary when removing a source

Having the summary pop up automatically after a source icon has been
removed is pretty useless ("Hey, there was something interesting going
on, but you missed it and it's gone now, kthxbye").

https://bugzilla.gnome.org/show_bug.cgi?id=630939

js/ui/messageTray.js

@@ -1006,10 +1006,6 @@ MessageTray.prototype = {
         this._notificationQueue = newNotificationQueue;
 
         this._summary.remove_actor(this._summaryItems[index].actor);
-        if (this._summary.get_children().length > 0)
-            this._summaryNeedsToBeShown = true;
-        else
-            this._summaryNeedsToBeShown = false;
 
         this._summaryItems.splice(index, 1);
         if (this._longestSummaryItem.source == source) {