Fix showing old notifications on groupless update

Fix issue where if notifications were shown as heads-up style and a 4th
notification is displayed all previous notifications would show again.

We need to regenerate these notifications to attach a group but we
didn't use setOnlyAlertOnce(true) to prevent showing as heads up again.

Author: jkasten2

OneSignalSDK/onesignal/src/main/java/com/onesignal/OneSignalNotificationManager.java

@@ -113,6 +113,7 @@ static void assignGrouplessNotifications(Context context, ArrayList<StatusBarNot
             // Recreate the notification but with the groupless key instead
             Notification notif = grouplessNotifBuilder
                     .setGroup(GROUPLESS_SUMMARY_KEY)
+                    .setOnlyAlertOnce(true)
                     .build();
 
             NotificationManagerCompat.from(context).notify(grouplessNotif.getId(), notif);