[libxslt] Remove obsolete AC_HEADER_STDC autoconf macro

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 6f4a633904614a60748372c225ee8abe5aae9018
Author: Vadim Zeitlin <vadim zeitlins org>
Date:   Thu Mar 10 00:45:28 2022 +0100

    Remove obsolete AC_HEADER_STDC autoconf macro
    
    It does nothing useful since a long time any more and just triggers
    warnings from autoconf 2.71 and later.

 configure.ac | 2 --
 1 file changed, 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 164b92c2..7748cf98 100644
--- a/configure.ac
+++ b/configure.ac
@@ -108,8 +108,6 @@ AC_PATH_PROG(XMLLINT, xmllint, /usr/bin/xmllint)
 AC_PATH_PROG(XSLTPROC, xsltproc, /usr/bin/xsltproc)
 PKG_PROG_PKG_CONFIG
 
-AC_HEADER_STDC
-
 LT_INIT(win32-dll)