Small fixes to basic classes and refactorings

Small fixes to basic classes and refactorings noticed while preparing a
later change. These changes are fairly "obvious" fixes and refactorings,
removed from the later change to make it smaller.

Test: atest services/tests/servicestests/src/com/android/server/timezonedetector/
Bug: 149014708
Change-Id: If9bcb567778d82f49b3481c50a64c0d739ce2ace