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 331b61794982778acd140eeae5047730072c93d5)
(cherry picked from commit adf4be190e39691c99578ee01fc3b19ca0dd16d1)
Merged-In:I9db781c300e96e9c80bd5d21585b8be9b4db08c8
2 files changed