Refactoring: Use explicit methods for checking DO/PO

Do not use USES_POLICY_PROFILE_OWNER / USES_POLICY_DEVICE_OWNER.
Instead, use explicit methods for checking if the caller is
the Device Owner or Profile Owner.

USES_POLICY_PROFILE_OWNER is confusing since internally in the
DevicePolicyManagerService, it implied a Device Owner is also a
Profile Owner, which is not always what the caller expected.

This is the first phase of the refactoring, removing external calles'
dependency on these constants. The next phase will remove them
internally completely in favour of an implementation that
accesses mOwners directly.

There are no functional changes in this CL.

Bug: 163028934
Test: atest FrameworksServicesTests:DevicePolicyManagerTest
Change-Id: I57c8465d190a3b4b130d57fd622cc93eaeb9c717