Remove workaround for bug in Linux kernel 2.6.8 or thereabouts.
The workaround isn't strictly needed for POSIX conformance, and
it's too much of a pain to configure and maintain. We'll ask
people to fix their kernels instead.
* modules/xnanosleep (Depends-on): Remove gethrxtime.
* lib/xnanosleep.c: Don't include gethrxtime.h or xtime.h.
(NANOSLEEP_BUG_WORKAROUND): Remove.
(xnanosleep): Remove the workaround.
* m4/xnanosleep.m4 (gl_XNANOSLEEP): Remove configuration attempting
to detect nanosleep bug.