Remove base class / rename Controller classes

Refactoring change before an upcoming behavior change commit.

The LocationTimeZoneProviderController class isn't pulling its weight,
so the ControllerImpl has been merged into it.

The support classes ControllerCallbackImpl and ControllerEnvironmentImpl
classes have been renamed to be prefixed by LocationTimeZone for
consistency.

Test: build / treehugger
Bug: 200279201
Change-Id: I9757edfe878d24546b2e82e5e761aea47e6a0679