build: Remove redundant .m4 file.
* gettext-runtime/intl/configure.ac: Don't invoke gl_AC_HEADER_STDINT_H.
* gettext-runtime/m4/stdint_h.m4: Remove file.
* gettext-runtime/m4/Makefile.am (EXTRA_DIST): Remove it.
* Makefile.am (distcheck-hook): Don't check it.
