gettimeofday() and settimeofday(): Move gittimeofdady() from sched/clock to...

gettimeofday() and settimeofday():  Move gittimeofdady() from sched/clock to libc/time.  All remove gettimeofday() from NuttX system calls.  It is only a wrapper around clock_settime() and does not need a trap.  gettimeofday() is no longer tried as a core OS interface.

gettimeofday has been decremented in POSIX 2008.  settimeofday() was never part of POSIX, but I decided to add it to libc as well just for symmetry.