Ensure proper return when revoking revoked group

Ensure that, when revoking the permission of a group that is already
revoked, the grant state is not set to "true" by default.

Test: Revoke a group with an already revoked permission. The returned
LightAppPermGroup should not have the already revoked permissions listed
as granted.

Change-Id: Ic3a7094d244b4422df954faf64ceea9d7acdcec9