DPC can be uninstalled in personal profile in New COPE

* For an organization-owned device, the DPC should be able to
  be uninstalled in the personal profile. Previously, the
  observed behaviour was that the uninstall button in the App
  Info Screen was being greyed out.
* This was because the previous logic did not allow for
  uninstalling any app which has a profile owner or device
  owner on *any* user.
* This CL updates this logic, such that, for non-system apps
  uninstalling is blocked only if the app has a profile owner
  or device owner for the current calling user.

Bug: 149381804
Test: Manual testing
      atest com.android.settings.applications.appinfo.AppButtonsPreferenceControllerTest
Change-Id: Ifaf03daa41724dbbd869c7e1371a77cc39d15ac7