Remove PasswordMetrics.validatePasswordMetrics isPin param

* Remove isPin parameter and use actualMetrics.credType,
  which now includes CREDENTIAL_TYPE_PIN

Bug: 184103377
Test: manual testing
      atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.cts.devicepolicy.ProfileOwnerTest
      atest com.android.cts.devicepolicy.MixedManagedProfileOwnerTest
      atest com.android.cts.devicepolicy.MixedManagedProfileOwnerTest
Change-Id: Ib79856b14981ef715c941e3cd56bd29ca196f3bb