Fix out-of-source make-dist problems

Fix out-of-source make-dist problems

Problem with jisx2131-filter reported by Phillip Lord in:
https://lists.gnu.org/r/emacs-devel/2019-06/msg00147.html
* admin/charsets/Makefile.in (SED_SCRIPT):
Put it in $(srcdir), which is not necessarily the working directory.
($(SED_SCRIPT)): Rename from jisx2131-filter.  All uses changed.
(clean): Do not remove SED_SCRIPT.
(extraclean): Remove it here instead.
* make-dist (possibly_non_vc_files): Remove src/emacs-module.h.
Although it is portable and could be distributed in the tarball,
it's too much hassle to do that, so let each builder make it.