Check group channels for FGSes

Before allowing the group to be deleted, by updating
the current check to the method that populates the channel
list

Test: NotificationManagerServiceTest
Bug: 209965481
Change-Id: I9db781c300e96e9c80bd5d21585b8be9b4db08c8
Merged-In: I9db781c300e96e9c80bd5d21585b8be9b4db08c8
(cherry picked from commit 6456b622fd39115001478b6fad2f45f50b65f30a)
Merged-In:I9db781c300e96e9c80bd5d21585b8be9b4db08c8
2 files changed