Remove NOTIFICATION_GROUP_EXPANSION_CHANGE flag.

Also did some test cleanup while at it:
- made the tests I updated multivalent, so they can run without a device
- removed redundant "test" from test names
- moved EntryUtil and GroupEntryBuilder to the utils directory where
  they belong (otherwise the tests didn't have access to them from the
  new location)

Fix: 292213543
Test: GroupExpansionManagerTest GroupMembershipManagerTest
Flag: LEGACY NOTIFICATION_GROUP_EXPANSION_CHANGE ENABLED

Change-Id: I01068bf98fc0942645079de3b2deeb58f65435eb