maint: remove useless REPLACE_*_H macros

maint: remove useless REPLACE_*_H macros

There are still a few modules, like iconv_h.m4, that still
use older paradigms where GNULIB_POSIXCHECK is unsupported
and where gl_REPLACE_<HEADER>_H is still essential.  But since
we are moving away from that style, I see no reason to keep
the idiom for the modules that don't need it.

* m4/arpa_inet_h.m4 (gl_REPLACE_ARPA_INET_H): Delete.
* m4/dirent_h.m4 (gl_REPLACE_DIRENT_H): Likewise.
* m4/locale_h.m4 (gl_REPLACE_LOCALE_H): Likewise.
* m4/poll_h.m4 (gl_REPLACE_POLL_H): Likewise.
* m4/spawn_h.m4 (gl_REPLACE_SPAWN_H): Likewise.
* m4/sys_ioctl_h.m4 (gl_REPLACE_SYS_IOCTL_H): Likewise.
* m4/wchar_h.m4 (gl_REPLACE_WCHAR_H): Likewise.
* m4/btowc.m4: Update callers.
* m4/dirfd.m4: Likewise.
* m4/duplocale.m4: Likewise.
* m4/fchdir.m4: Likewise.
* m4/fdopendir.m4: Likewise.
* m4/inet_ntop.m4: Likewise.
* m4/inet_pton.m4: Likewise.
* m4/ioctl.m4: Likewise.
* m4/mbrlen.m4: Likewise.
* m4/mbrtowc.m4: Likewise.
* m4/mbsinit.m4: Likewise.
* m4/mbsnrtowcs.m4: Likewise.
* m4/mbsrtowcs.m4: Likewise.
* m4/poll.m4: Likewise.
* m4/setlocale.m4: Likewise.
* m4/wcrtomb.m4: Likewise.
* m4/wcsnrtombs.m4: Likewise.
* m4/wcsrtombs.m4: Likewise.
* m4/wctob.m4: Likewise.
* m4/wcwidth.m4: Likewise.
* modules/posix_spawn: Likewise.
* modules/posix_spawn_file_actions_addclose: Likewise.
* modules/posix_spawn_file_actions_adddup2: Likewise.
* modules/posix_spawn_file_actions_addopen: Likewise.
* modules/posix_spawn_file_actions_destroy: Likewise.
* modules/posix_spawn_file_actions_init: Likewise.
* modules/posix_spawnattr_destroy: Likewise.
* modules/posix_spawnattr_getflags: Likewise.
* modules/posix_spawnattr_getpgroup: Likewise.
* modules/posix_spawnattr_getschedparam: Likewise.
* modules/posix_spawnattr_getschedpolicy: Likewise.
* modules/posix_spawnattr_getsigdefault: Likewise.
* modules/posix_spawnattr_getsigmask: Likewise.
* modules/posix_spawnattr_init: Likewise.
* modules/posix_spawnattr_setflags: Likewise.
* modules/posix_spawnattr_setpgroup: Likewise.
* modules/posix_spawnattr_setschedparam: Likewise.
* modules/posix_spawnattr_setschedpolicy: Likewise.
* modules/posix_spawnattr_setsigdefault: Likewise.
* modules/posix_spawnattr_setsigmask: Likewise.
* modules/posix_spawnp: Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>