overviewControls: Remove message indicator

The message tray is now empty and about to be removed, so an indication
at the bottom edge of the overview becomes an odd location to convey the
status of the summary. We will eventually display an indication in the
top bar that unseen messages are available, for now just remove the
existing indicator.

https://bugzilla.gnome.org/show_bug.cgi?id=744850

js/ui/messageTray.js

@@ -1255,11 +1255,6 @@ const Source = new Lang.Class({
         return this.notifications.length;
     },
 
-    get indicatorCount() {
-        let notifications = this.notifications.filter(function(n) { return !n.isTransient && !n.resident; });
-        return notifications.length;
-    },
-
     get unseenCount() {
         return this.notifications.filter(function(n) { return !n.acknowledged; }).length;
     },