Refactoring: Move code to StatsPullAtomService

Refactoring: Move time zone detection metrics byte[] generation code to
StatsPullAtomService so it's clearer what information is sent off of the
device. Previously, the byte[] was generated in service code
(MetricsTimeZoneDetectorState), which means that changes don't require
metrics team OWNERS approval and changes could be missed.

This change is a refactoring before an upcoming addition to the byte[]
content is actually made.

Bug: 200279201
Test: build only
Change-Id: I79a03580b204b78cfb9f969f460d1fd8475befdb