timer.h: remove unneeded include (sys/timeb.h)

not only is the header not needed, it was obsoleted in posix
and thus is missing in musl libc.
timer.h: re-add sys/timeb.h to windows section

it's unneeded on windows as well but the ppl in charge want to
play safe. so do as they want and make them happy. *shrug*
Merge pull request #247 from rofl0r/timeb

timer.h: remove unneeded include (sys/timeb.h)