SetupWizard: Use SettingsLib for Timezones

* Currently we are storing a copy of timezones.xml ourselves and parsing
  it manually
* Use ZoneGetter from SettingsLib instead to get the list of TimeZones
* That way we have less code to maintain and updates to the list are easier
  as well
* Also simplify constructTimezoneAdapter -> we never sort by name

Change-Id: Ifd690ed28c6fbecaee895b4063137e86c059e314