UM.getAliveUsers to exclude initialised ephemeral noncurrent users.

When the device is rebooted while an ephemeral user is in foreground,
after the reboot UserManager.getAliveUsers() was containing that user
as well, which was causing a FATAL exception in BiometricScheduler
during boot.

This CL fixes that issue by excluding the initialised ephemeral
non-current users from UserManager.getAliveUsers().

Bug: 327972305
Test: atest UserManagerServiceTest#testGetAliveUsers_shouldExcludeInitialisedEphemeralNonCurrentUsers
Flag: None
Change-Id: I44cbb1e27e1aa84a5f78786d9e05d02a029fa5b3