Handle removal of time_zones_by_country.xml

The time_zones_by_country.xml file has been replaced
by a file that can be updated outside of an OTA and
can be accessed via libcore.util.TimeZoneFinder.

This change includes refactorings that result
and keeps this code from using ICU types to avoid
confusion.

Bug: 25338903
Test: Ran CtsUtilTestCases
Change-Id: I699b4e7420e8d7e61ee68ec96552ab3144c9bab2