build: Remove some duplicate .m4 files.
* autogen.sh: Copy wchar_t.m4 and wint_t.m4 for libasprintf.
* gettext-runtime/m4/codeset.m4: Remove file.
* gettext-runtime/m4/extern-inline.m4: Remove file.
* gettext-runtime/m4/intl-thread-locale.m4: Remove file.
* gettext-runtime/m4/lcmessage.m4: Remove file.
* gettext-runtime/m4/lock.m4: Remove file.
* gettext-runtime/m4/longlong.m4: Remove file.
* gettext-runtime/m4/threadlib.m4: Remove file.
* gettext-runtime/m4/wchar_t.m4: Remove file.
* gettext-runtime/m4/wint_t.m4: Remove file.
* gettext-runtime/m4/Makefile.am (EXTRA_DIST): Don't distribute them.
* Makefile.am (distcheck-hook): Don't verify that they are identical copies.
