[libxml2] Remove obsolete AC_HEADER checks

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 5c009c668b5b8ae90e274d75f5cbb658d0901482
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Wed Mar 2 01:31:56 2022 +0100

    Remove obsolete AC_HEADER checks

 configure.ac | 2 --
 1 file changed, 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 1748b07d..5f9dfa78 100644
--- a/configure.ac
+++ b/configure.ac
@@ -442,8 +442,6 @@ LIBS=${_libs}
 echo Checking headers
 
 dnl Checks for header files.
-AC_HEADER_DIRENT
-AC_HEADER_STDC
 AC_CHECK_HEADERS([fcntl.h])
 AC_CHECK_HEADERS([unistd.h])
 AC_CHECK_HEADERS([sys/stat.h])