nxwitness-client: switch to libxml2_13 that has patches for 5 CVEs (#434428)

pkgs/by-name/nx/nxwitness-client/package.nix

@@ -12,7 +12,7 @@
   libudev-zero,
   libxcb,
   libxkbfile,
-  libxml2,
+  libxml2_13,
   libxslt,
   openal,
   qt6Packages,
@@ -26,19 +26,6 @@ let
   version = "6.0.3";
   build = "40736";
 
-  libxml2_13 = libxml2.overrideAttrs (oldAttrs: rec {
-    version = "2.13.8";
-    src = fetchurl {
-      url = "mirror://gnome/sources/libxml2/${lib.versions.majorMinor version}/libxml2-${version}.tar.xz";
-      hash = "sha256-J3KUyzMRmrcbK8gfL0Rem8lDW4k60VuyzSsOhZoO6Eo=";
-    };
-    meta = oldAttrs.meta // {
-      knownVulnerabilities = oldAttrs.meta.knownVulnerabilities or [ ] ++ [
-        "CVE-2025-6021"
-      ];
-    };
-  });
-
   buildInputs = [
     glib
     gst_all_1.gst-plugins-base