Disable setting if sensor is convenience.

This change disables the FaceSettings Confirmation setting if a
sensor is convenience. This is due to the fact that convenience strength
sensors can't be used by BiometricPrompt (so this setting has no
effect.)

Test: Verified this setting shows depending on whether or not the sensor
is convenience or not.
Fixes: 204137656

Change-Id: I88daf9f12b76d06697275161385f463fb88e0f3a