CameraService: hold onto SensorPrivacyManager

unlinkToDeath is no longer required, (this change in behavior is to
avoid leaks) so holding onto the service here (still calling
unlinkToDeath to avoid a log, but may for instance remove all
unlinkToDeath calls in the future).

Bug: 145692765
Test: boot, see linkToDeath maintained
Change-Id: Ib74ab470580643ff61fc684fdd4e16d5e38389af