Remove separate background for managed profiles

This change removes the managed profile background to address the two
issues below:
1) When one-lock is enabled, the credential UI will no longer incorrectly
   show the managed profile background. This bug was introduced when
   credential authentication UI was moved to SystemUI
2) The new managed profile authentication UX no longer uses a separate
   background

Fixes: 147653255
Bug: 141290838

Test: atest com.android.systemui.biometrics

Change-Id: Ib48f5e5c97c4c16c430625864377a001e100de1a