remove obsolete notification visibility log

        @Override

        public void onNotificationVisibilityChanged(

                String[] newlyVisibleKeys, String[] noLongerVisibleKeys) {

            // Using ';' as separator since eventlogs uses ',' to separate

            // args.

            // TODO remove this: b/21248682

            EventLogTags.writeNotificationVisibilityChanged(

                    TextUtils.join(";", newlyVisibleKeys),

                    TextUtils.join(";", noLongerVisibleKeys));

            synchronized (mNotificationList) {

                for (String key : newlyVisibleKeys) {

                    NotificationRecord r = mNotificationsByKey.get(key);