Remove remainder of generateChallengeBlocking

Test: make -j56 RunSettingsRoboTests

Face Tests:
Test: Open face settings, remove face, add face
Test: Open face settings, but cancel credential confirmation.
      Face settings does not show up
Test: adb shell am start -a android.app.action.SET_NEW_PASSWORD
      Able to enroll face

Fingerprint Tests:
Test: Open fingerprint settings, add button is shown
Test: Open fingerprint settings, but cancel credential confirmation.
      Fingerprint settings does not show up
Test: adb shell am start -a android.app.action.SET_NEW_PASSWORD
      Able to enroll fingerprint

Bug: 162533680
Change-Id: Ie448ed086e73b0b545bd3a2e62437c543f7aad6c