Update KUM usage of primaryUser to systemUser

KeyguardUpdateMonitor only wants to run fingerprint
and face listening state from the systemUser. PrimaryUser
usage is deprecated.

The DeviceEntryFaceAuthRepository doesn't need to check for
the primary user. Instead, the FaceAuth triggers should only
be running in the system user (as all SystemUI CoreStartables
are done that aren't "@PerUser").

Test: atest KeyguardUpdateMonitorTest DeviceEntryFaceAuthRepositoryTest
Bug: 264869291
Change-Id: Idb49fc652182bcba9393af3c7b1f1eb968e417e3