Individual sensor services only need to keep track of their
ID. When doing things that require knowledge of current strength,
query BiometricService.
Bug: 149067920
Fixes: 151953729
Test: atest com.android.server.biometrics
Test: BiometricPromptDemo
Change-Id: Id2b7cd4e02c1a4b4707950285923f8166b8f46e1