When channels are deleted, remove notifications from recently dismissed list.

This change adds a function to Archive to remove all notifications associated with a specific user & channel, and also modifies notification cancellation to not record the notifications in mArchive if the cancellation reason is that the entire channel was removed.

Test: atest ArchiveTest, NotificationManagerServiceTest, and manual confirmation
Fixes: 169349809

Change-Id: Id4f678534f1c26243b99740e2954b5d54591f110