Modify DevicePolicyManagerService to extend IDevicePolicyManager.aidl

Problem: ArcDevicePolicyManagerService extends BaseIDevicePolicyManager which is an abstract class that defines the required interface for IDevicePolicyManager.aidl.
Whenever a method is added to IDevicePolicyManager.aidl, an empty override method should be added in BaseIDevicePolicyManager to avoid build breakage in downstream branches. But since upstream developers are mostly unaware of this class, that doesn’t happen leading to build failures in ARC.

Solution: DevicePolicyManagerService extends IDevicePolicyManager.aidl instead of BaseIDevicePolicyManager and we remove BaseIDevicePolicyManager altogether
Design Doc: http://doc/1rGmymvoKZCn3H2Gbic5cnlgyZJo8ZtlgDzX5o0sG4zE

Bug: 187842408
Test: atest CtsDevicePolicyTestCases
Test: tast run DUT enterprise.ARCProvisioning.vm
Change-Id: I80ab8fd1be197e0dfa146836d4b65bc13db24740