Reduce nt and src Makefile duplication wrt emacs.res

* nt/Makefile.in (../src/emacs.res): New target.

* src/Makefile.in (emacs.res): Use ../nt rule, rather than duplicating it.
(ntsource, WINDRES, EMACS_MANIFEST): Remove, now unused.
* src/emacs.c (main) <--version>: Make use of PACKAGE_NAME.