tools: drop bogus and obsolete ptyfuncs.m4

According to openpty(3) it is required to include <pty.h> to get the
prototypes for openpty() and login_tty(). But this is not what the
function AX_CHECK_PTYFUNCS actually does. It makes no attempt to include
the required header.

The two source files which call openpty() and login_tty() already contain
the conditionals to include the required header.

Remove the bogus m4 file to fix build with clang, which complains about
calls to undeclared functions.

Remove usage of INCLUDE_LIBUTIL_H in libxl_bootloader.c, it is already
covered by inclusion of libxl_osdep.h.

Remove usage of PTYFUNCS_LIBS in libxl/Makefile, it is already covered
by UTIL_LIBS from config/StdGNU.mk.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

m4/ptyfuncs.m4

@@ -1,35 +0,0 @@
-AC_DEFUN([AX_CHECK_PTYFUNCS], [
-    dnl This is a workaround for a bug in Debian package
-    dnl libbsd-dev-0.3.0-1. Once we no longer support that
-    dnl package we can remove the addition of -Werror to
-    dnl CPPFLAGS.
-    AX_SAVEVAR_SAVE(CPPFLAGS)
-    CPPFLAGS="$CPPFLAGS -Werror"
-    AC_CHECK_HEADER([libutil.h],[
-      AC_DEFINE([INCLUDE_LIBUTIL_H],[<libutil.h>],[libutil header file name])
-    ])
-    AX_SAVEVAR_RESTORE(CPPFLAGS)
-    AC_CACHE_CHECK([for openpty et al], [ax_cv_ptyfuncs_libs], [
-        for ax_cv_ptyfuncs_libs in -lutil "" NOT_FOUND; do
-            if test "x$ax_cv_ptyfuncs_libs" = "xNOT_FOUND"; then
-                AC_MSG_FAILURE([Unable to find library for openpty and login_tty])
-            fi
-            AX_SAVEVAR_SAVE(LIBS)
-            LIBS="$LIBS $ax_cv_ptyfuncs_libs"
-            AC_LINK_IFELSE([AC_LANG_SOURCE([
-#ifdef INCLUDE_LIBUTIL_H
-#include INCLUDE_LIBUTIL_H
-#endif
-int main(void) {
-  openpty(0,0,0,0,0);
-  login_tty(0);
-}
-])],[
-                break
-            ],[])
-            AX_SAVEVAR_RESTORE(LIBS)
-        done
-    ])
-    PTYFUNCS_LIBS="$ax_cv_ptyfuncs_libs"
-    AC_SUBST(PTYFUNCS_LIBS)
-])