chrome: drop visibleInOverview

Every place that called chrome.addActor was specifying
visibleInOverview:true, and no existing designs call for chrome that
disappears when you enter the overview, so just drop that as an
option.

https://bugzilla.gnome.org/show_bug.cgi?id=633620

js/ui/messageTray.js

@@ -1252,7 +1252,6 @@ MessageTray.prototype = {
         this._reNotifyAfterHideNotification = null;
 
         Main.chrome.addActor(this.actor, { affectsStruts: false,
-                                           visibleInOverview: true,
                                            visibleInFullscreen: true });
         Main.chrome.trackActor(this._notificationBin);
         Main.chrome.trackActor(this._summaryBoxPointer.actor);