Fixing the FCM notification sample so that it waits for every token deletes.
Fixing the FCM notification sample so that it waits for every token deletes.

Change-Id: Idf9a964a50d3d0f48ed720aa403353167d208542

Kevded/functions-samples,firebase/functions-samples,firebase/functions-samples,firebase/functions-samples,firebase/functions-samples,Kevded/functions-samples,Kevded/functions-samples,Kevded/functions-samples