Animate away instead of suddenly disappearing

In certain cases, such as when callers cancel authentication,
we are not animating away nicely. This fixes it.

Bug: 152240892
Test: atest android.server.biometrics.BiometricSimpleTests#testBiometricCancellation
Change-Id: I7e23de1453856afa2aec877792f8bdb76475d592
1 file changed