system: Hide the Log Out / Switch User items in the lock screen

https://bugzilla.gnome.org/show_bug.cgi?id=705845

js/ui/status/system.js

@@ -100,6 +100,7 @@ const Indicator = new Lang.Class({
     _sessionUpdated: function() {
         this._updateLockScreen();
         this._updatePowerOff();
+        this._updateMultiUser();
         this._settingsAction.visible = Main.sessionMode.allowSettings;
     },