Also start the FetchForegroundService in onDeletedMessages() (#3317)

See https://firebase.google.com/docs/cloud-messaging/android/receive#override-ondeletedmessages

Shouldn't happen very often, but if it does, it's good to connect, too.

src/gplay/java/org/thoughtcrime/securesms/notifications/FcmReceiveService.java

@@ -102,7 +102,7 @@ public class FcmReceiveService extends FirebaseMessagingService {
   @Override
   public void onDeletedMessages() {
     Log.i(TAG, "FCM push notifications dropped");
-    // nothing special to do as we're running now and notifications should be processed as usual.
+    FetchForegroundService.start(this);
   }
 
   @Override