Removes HIDL references from ContextHubService

This CL fully encapsulates HIDL references in the IContextHubWrapper,
allowing the ContextHubService to operate independently regardless of
whether the HAL is HIDL/AIDL.

Bug: 194285834
Test: Presubmits, run CHQTS on device
Test: Manual testing of untested code path (e.g. Context Hub restart)
Change-Id: I56494a4bd5f508601b8a0f4e3ab1c74a858b81f2