Use userId 0 to bind the DisplayHashingService

Clear calling identity and use system user id to bind the service. This
is because the DisplayHashingSevice doesn't need to be run per user and
can just be run as system.

Test: atest DisplayHashManagerTest
Bug: 184783122
Change-Id: Id15efeddefff632e339139899a17a550e517dd5b
1 file changed