Suppress msgs from FACE_ERROR_UNABLE_TO_PROCESS

Don't surface error messages on the lock screen
for FACE_ERROR_UNABLE_TO_PROCESS. After 500ms
from receiving this error, keyguard attempts
to face auth again anyway (see
KeyguardUpdateMonitor#HAL_ERROR_RETRY_ERROR_TIMEOUT).

Test: atest KeyguardIndicationControllerTest
Test: enroll face, press power button to LS,
use camera app, then navigate back to LS, don't
see the UNABLE_TO_PROCESS error.
Bug: 223768181

Change-Id: I0eb017f5e5f31d8fabf36876ea0949050a9f5f58