pipe-filter-gi, pipe-filter-ii: Silence -Wunused-macro warning

[Bruno Haible]

The gcc -Wunused-macros warning option triggers many warnings, too many to
regularly look at. But occasionally, it highlights code that can be cleaned up.
Such as this one:

gettext-tools/gnulib-lib/pipe-filter-aux.c:40: warning: macro "_" is not used


2023-06-02  Bruno Haible  <bruno@clisp.org>

        pipe-filter-gi, pipe-filter-ii: Silence -Wunused-macro warning.
        * lib/pipe-filter-aux.c: Remove many unnecessary includes.
        (_): Remove macro.

diff --git a/lib/pipe-filter-aux.c b/lib/pipe-filter-aux.c
index 5fc7758449..1da31a723f 100644
--- a/lib/pipe-filter-aux.c
+++ b/lib/pipe-filter-aux.c
@@ -21,22 +21,6 @@
 #include "pipe-filter.h"
 
 #include <errno.h>
-#include <fcntl.h>
-#include <stdint.h>
-#include <stdlib.h>
 #include <unistd.h>
-#if defined _WIN32 && ! defined __CYGWIN__
-# include <windows.h>
-#else
-# include <signal.h>
-# include <sys/select.h>
-#endif
-
-#include "error.h"
-#include "spawn-pipe.h"
-#include "wait-process.h"
-#include "gettext.h"
-
-#define _(str) gettext (str)
 
 #include "pipe-filter-aux.h"