Allow pullAtomCallbacks to be unregistered in Java

Adds an API to unregister pullAtomCallbacks.
Fixes bug where the StatsEventParcels are null.
Makes onPullAtom a oneway call.
OnPullAtom returns an int code instead of a boolean
Made the APIs return RuntimeExceptions

Test: make, boots
Test: atest GtsStatsdHostTestCases
Bug: 146385842
Bug: 146385173
Bug: 144373250
Change-Id: I107a705a9024240c5c9f9e276293de8410e2b6f3