GCM to FCM InstanceID and duplicate token issue

[Luca Looz]

I'm trying to switch to FCM but when i remove GCM and use the new FirebaseInstanceId api i notice that a new token and instance id are generated and the old one of "play-services-iid" aren't invalidated.

So on my server i get 2 valid token for the same device that will cause a duplicate notification without a not registered error or a canonical id response