Remove HAVE_STDIO_H

The `<stdio.h>` header file is part of the standard C89 headers [1]
and on current systems can be included unconditionally.

Since PHP requires at least C89 or greater, the `HAVE_STDIO_H` symbol
defined by Autoconf [2] can be ommitted and simplifed.

Refs:
[1] https://port70.net/~nsz/c/c89/c89-draft.html#4.1.2
[2] https://git.savannah.gnu.org/cgit/autoconf.git/tree/lib/autoconf/headers.m4

Author: petk

ext/mbstring/libmbfl/config.h.w32

@@ -1,4 +1,3 @@
-#define HAVE_STDIO_H 1
 #define HAVE_MEMORY_H 1
 /* #undef HAVE_STRINGS_H */
 #define HAVE_STRING_H 1

sapi/fpm/config.m4

@@ -11,7 +11,7 @@ AC_DEFUN([AC_FPM_STDLIBS],
   AC_SEARCH_LIBS(socket, socket)
   AC_SEARCH_LIBS(inet_addr, nsl)
 
-  AC_CHECK_HEADERS([fcntl.h stdio.h unistd.h sys/uio.h])
+  AC_CHECK_HEADERS([fcntl.h unistd.h sys/uio.h])
   AC_CHECK_HEADERS([sys/select.h sys/socket.h sys/time.h])
   AC_CHECK_HEADERS([arpa/inet.h netinet/in.h])
   AC_CHECK_HEADERS([sysexits.h])