Get rid of the redundant shim interfaces

It was agred to expose gd types into the system/bt/main folder.
All the interfaces already use pimpl pattern to make them testable.
Thus there is no need for the I* shim interfaces.

Test: updated tests
Bug: 149757450
Change-Id: I9662f9ab48c61b764e4df082da1a73483cb0b2b9