Re-activate backup service after cleaning a profile owner

Currently backup service is re-activated unconditionally when clearing
a device owner but not profile owner. With this CL it should be
re-activate in both cases.

NB: there are two bits of state related to backup service:
1. activated or deactivated: This is out of user control, but can be
   changed by the admin via DPM.setBackupServiceEnabled (this name is
   a bit misleading here).
2. enabled or disabled: this is controlled by the user via Settings
   and only available when backup service is activated (see 1.)

Bug: 143274029
Test: atest CtsAdminTestCases && adb shell bmgr enabled
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
Change-Id: I6f11642abe544c7df265ed7e2ad466d47796e7f9