Support programs like Emacs that use gnulib but not gettext.

Support programs like Emacs that use gnulib but not gettext.
* MODULES.html.sh (Internationalization functions): Add gettext-h.
* modules/gettext-h: New file.
* modules/gettext (Files): Remove lib/gettext.h.
(Depends-on): Add gettext-h.
(Makefile.am): Remove lib_SOURCES.
* modules/argmatch, modules/c-stack, modules/closeout:
* modules/copy-file, modules/csharpcomp, modules/csharpexec:
* modules/execute, modules/file-type, modules/getaddrinfo:
* modules/getopt, modules/human, modules/javacomp:
* modules/javaexec, modules/mkdir-p, modules/obstack:
* modules/openat, modules/pagealign_alloc, modules/pipe:
* modules/quotearg, modules/regex, modules/rpmatch:
* modules/unicodeio, modules/userspec, modules/version-etc:
* modules/wait-process, modules/xalloc-die, modules/xmemcoll:
* modules/xsetenv:
Depend on gettext-h, not gettext.