build: Assume that <stdint.h> or <inttypes.h> defines uintmax_t.
OpenBSD has it since OpenBSD 3.9 (2006).
* gettext-runtime/m4/intl.m4 (gt_INTL_SUBDIR_CORE): Don't invoke
gl_AC_TYPE_UINTMAX_T.
* gettext-runtime/m4/uintmax_t.m4: Remove file.
* gettext-runtime/m4/Makefile.am (EXTRA_DIST): Remove it.
