Remove onWindowFocusChange solution from FPS enrollment

Context:
The legacy architecture UdfpsEnrollView was shown by SysUI
which has higher z-order that encounter lots of overlap issue.
Besides, IPC impact the latency of show/hide enroll view in
legacy architecture.
We used to upload ag/19699461 to cancel enrollment due to
above limitation.

With the new architecture ag/20582186 the UdfpsEnrollView
migrate to Settings and controlled by Settings process.

And ag/21149538 config SETTINGS_SHOW_UDFPS_ENROLL_IN_SETTINGS flag
to ture by default.

It's the time to improve the enroll UX by removing cancel
signle when onWindowFocusChanged() invoked.

Bug: 262680438
Test: m RunSettingsRoboTests -j30 ROBOTEST_FILTER=FingerprintEnrollEnrollingTest
Test: manual Security Settings > Enroll fingerprint > enroll
      Swipe Notify Shade , Heads-up, Power menu interrupt should
      not stop the enroll flow.
Change-Id: I60d88d5edd80e6eed70e2fbf288357e949abcae3

tests/robotests/src/com/android/settings/biometrics/fingerprint/FingerprintEnrollEnrollingTest.java

@@ -158,7 +158,7 @@ public class FingerprintEnrollEnrollingTest {
     }
 
     @Test
-    public void fingerprintUdfpsOverlayEnrollment_loseFocus_shouldCancel() {
+    public void fingerprintUdfpsOverlayEnrollment_loseFocus_shouldNotCancel() {
         initializeActivityFor(TYPE_UDFPS_OPTICAL);
 
         mActivity.onEnrollmentProgressChange(1, 1);