Fix back navigation in biometric enrollment.

Using the back buttons can cause a crash in at least two cases. Skipping
face enrollment and then starting/stopping any enrollment can lead to
an invalid token and failed HAT request. Backing out of the activity and
restarting it can also lead to using a stale token that fails.

Fix: 179336333
Test: manual on device
Change-Id: I0c1133e4c3d9c97997043ddc9374aa3cfc4f1c97

src/com/android/settings/biometrics/fingerprint/FingerprintEnrollFindSensor.java

@@ -85,7 +85,6 @@ public class FingerprintEnrollFindSensor extends BiometricEnrollBase implements
                 mChallenge = challenge;
                 mSensorId = sensorId;
                 mToken = BiometricUtils.requestGatekeeperHat(this, getIntent(), mUserId, challenge);
-                BiometricUtils.removeGatekeeperPasswordHandle(this, getIntent());
 
                 // Put this into the intent. This is really just to work around the fact that the
                 // enrollment sidecar gets the HAT from the activity's intent, rather than having