fdoNotificationDaemon: Don't reshow a banner for updated notifications

There is arguably some room for interpretation but the notification
specs suggest that a notification should be updated without any "visual
cues" therefore the notification shouldn't show a banner again when it's
replaced.

js/ui/notificationDaemon.js

@@ -206,7 +206,6 @@ class FdoNotificationDaemon {
             gicon,
             useBodyMarkup: true,
             sound: new MessageTray.Sound(soundFile, hints['sound-name']),
-            acknowledged: false,
         });
         notification.clearActions();