Merge pull request #2967 from nextcloud/removeGCM

Remove gcm as we use firebase messaging

gplay.gradle

@@ -1,4 +1,3 @@
 dependencies {
-    implementation "com.google.firebase:firebase-messaging:17.1.0"
-    implementation "com.google.android.gms:play-services-gcm:15.0.1"
+    implementation "com.google.firebase:firebase-messaging:17.3.0"
 }