Handle case where ClientMonitors should not be started

Currently, the only case is when the HAL is null. For this, there are
two cases:

1) Non-BiometricPrompt operation
For these, clean up the current client, and do the same for any
operation that's currently pending. See code comments for more
details

2) BiometricPrompt operation
For these, just clean up the current BiometricPrompt operation

Fixes: 165636620
Test: atest BiometricSchedulerTest
Test: smoke test: enroll, auth on existing devices
Change-Id: Iff64d5dba8dc6ebd73f0f9fba233390e76ca8a89