Cleanup/refactoring pass on hwclock.

Cleanup/refactoring pass on hwclock.

Inline open_wall_clock_rtc() into rtc_open(), factor out xtzset(),
inline set_sysclock_from_hwclock(), set_hwclock_from_sysclock(),
and set_sysclock_timezone().

/etc/adjtime is short enough we don't need to bother with a break.

The final "else" case in main() should always trigger because >0 in optstr
says "at most zero arguments", so the || at the end is always true, so
take the test off.