Fix kotlin nullable errors in PermissionService.

This is meant to be a minimal fix for kotlin nullable error that was
exposed by setting the retention of android.annotation.NonNull and
android.annotation.Nullable to class retention by making it match the
PermissionManagerServiceInterface interface and not needed when
ag/23509136 is present.

Bug: 329087767
Test: builds
Merged-In: Ib3358be57d7dd401fd2014ade3e58f9fc6c2b6a7
Change-Id: I720bfa787a86966df8501b60cecf8c0726a919ef