1/n: Use scheduleForSensor instead of directly accessing scheduler

Minor cleanup that allows us to restrict access/usage of the scheduler
itself for cleaner and more robust future work. For example, if we
want to abstract the scheduler away from the AIDL provider.

Bug: 181984005
Test: atest CtsBiometricsTestCases
Change-Id: I5850cae1f30f9479a29565b7b7c0d43108d0f7bd