Remove redundant cancel events from FingerprintService

This fixes a bug where the framework was sending repeat cancel
events in response to terminal status (onAuthenticated(), onError())
which causes the underlying HAL implementation to get into a weird state.

Now, only client-initiated events like an explicit cancellation
or starting another authentication/enrollment invokes fingerprintd's
cancel() method.

Fixes bug 22438498

Change-Id: I762bab1c8635924848f9f4334db47a07130d5ae3