maint: remove m4sh support.
Now that the code base has coalesced around a single option
parser, there's no need for the unused getopt.m4sh and support.
* build-aux/getopt.m4sh, build-aux/general.m4sh,
tests/getopt-m4sh.at: Remove.
* Makefile.am (m4sh_dir, LT_M4SH, general_m4sh, getopt_m4sh)
(sh_files): Remove.
(TESTSUITE_AT): Remove tests/getopt-m4sh.at.
(TESTS_ENVIRONMENT): Remove M4SH.
* bootstrap.conf (libtool_build_prerequisites): Remove M4SH.
* configure.ac (M4SH): Remove.
* HACKING (Editing `.m4sh' Files): Remove and renumber following
sections.