Fix the flicker of FingerprintSettings before FingerprintEnrollIntro.

Change to launch FingerprintEnrollIntroductionInternal directly when no fingerprint enrolled and fingerprint is the only biometrics. This avoids the flicker of FingerPrintSettings before showing the enroll introduction.
This partially reverts the change in ag/19732076.

Bug: 256334588

Test: manual test following cases on fp-only devices, and enable don't
      keep activity and test them again.
      1. fp enrollment on SUW
      2. fp add another on SUW
      3. add first fp on Security Settings
      4. add another fp on Security Settings
Test: atest FingerprintStatusUtilsTest BiometricsSafetySourceTest

Change-Id: I057b00fbca6660012887ebedf4d65c2c3d35792b