Clear DateFormat.is24Hour during test.

TCKLocalizedPrinterParser checks if java.time.format.DateTimeFormatter
and java.text.DateFormat produce the same output for equivalent input.

java.text.DateFormat takes into account DateFormat.is24Hour which
represents a user-setting forcing a 12- or 24-hour clock. java.time
intentionally doesn't respect that, which causes this test to fail when
either a 12h or a 24h clock is forced.

This commits clears the setting for the duration of the test and re-sets
it to its orginal value afterwards.

Test: cts --primary-abi-only -m CtsLibcoreOjTestCases
Bug: 62651881
Change-Id: I30bab1d5f04cac8bdfc9a455c8ddc3ff39271077