hwclock: remove dead code and other minor fixes

hwclock: remove dead code and other minor fixes

Use #ifdef rather than #if to avoid undefined preprocessor identifier
warning.

Remove dead code.  The #if 0 ensured the code has not been used for long
time, which is good because the linux/mc146818rtc.h is not been part of
user-api for long time.

Value of the adjtime_p->last_calib_time is checked if it has value of zero,
so testing none-zero bit later is necessarily true, and therefore does not
need to be checked.

And at the and remove unnecessary boolean variable.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>