Rename SimpleTimeZoneDetectorStrategy

Rename SimpleTimeZoneDetectorStrategy to TimeZoneDetectorStrategyImpl.
Its defining characteristic is not simplicity - it's currently the
only implementation.

There are also some small cleanups around the
TimeDetectorStrategy.Callback not being needed by TimeDetectorService.

Bug: 140712361
Test: treehugger only
Change-Id: Icdf365a6a123574fb2cd21b89a9749a2f386c5fd