Minor changes on HsumBootUserInitializer and tests.

- Removed unused method.
- Moved tracing calls inside the method.
- Explicitly call expectSetBootUserId() when needed.
- Minor formating fixes that were skipped in the first CL.
- Removed redundant static keyword on enums

Test: atest FrameworksMockingServicesTests:HsumBootUserInitializerTest
Bug: 402486365
Flag: android.multiuser.create_initial_user

Change-Id: I6807d6ab12a16cc5a892d1bdca91a4fd3b761fe2