maint: remove fstimeprec (variable precision time stamp) support

maint: remove fstimeprec (variable precision time stamp) support

The implementation of variable-precision time stamps relied
on heuristics that made the output subtly nondeterministic,
or at least hard to reproduce:
http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/21531/focus=21538
So, for now at least, we're removing that feature.
* bootstrap.conf (gnulib_modules): Remove fstimeprec.
* gl/lib/fstimeprec.c, gl/lib/fstimeprec.h: Remove files.
* gl/modules/fstimeprec, gl/modules/fstimeprec-tests: Likewise.
* gl/tests/test-fstimeprec.c: Remove file.