Clean up interface between LocationManagerService and the location providers:

LocationManagerService now uses new Java interface LocationProviderInterface
rather than LocationProviderProxy to refer to location providers internally.

LocationProviderProxy and the ILocationProvider binder interface are only
used for location providers implemented as services (NetworkLocationProvider)

Built-in location providers (GpsLocationProvider and mock providers) now just
implement LocationProviderInterface rather than using a Binder interface and proxy object.

Delete obsolete and unused TestLocationProvider class.

Change-Id: Id800e7c1864f7c666f8e37125c05896493b9c8c4
Signed-off-by: Mike Lockwood <lockwood@android.com>