Make tz data files in the runtime module optional

Make time zone data files in the runtime mainline module optional:
the time zone data mainline module is now expected / required to
provide the files in all cases.

Bug: 132168458
Test: atest CtsLibcoreTestCases
Test: Ran "adb shell dumpsys runtime" and inspected
Change-Id: Ib559f1863843a8d9b28fff57472d8091ccdbc33e
6 files changed