Use new APIs to register/unregister network policy listener

For mainline support, remove usage of INetworkPolicyManager from
DcTracker. Use SubscriptionListener which be created a proxy
object in NetworkPolicyManger to register/unregister network
policy listener.

Bug: 138306002
Test: atest FrameworksNetTests
      atest FrameworksTelephonyTests

Change-Id: I1f191d36901001bd91218a19ee5d775cacdddff2