treewide: purge maintainers.urkud

It's sad, but he's been inactive for the last five years.
Keeping such people in meta.maintainers is counter-productive.

pkgs/development/libraries/clutter/default.nix

@@ -46,7 +46,7 @@ stdenv.mkDerivation rec {
     license = stdenv.lib.licenses.lgpl2Plus;
     homepage = http://www.clutter-project.org/;
 
-    maintainers = with stdenv.lib.maintainers; [ urkud lethalman ];
+    maintainers = with stdenv.lib.maintainers; [ lethalman ];
     platforms = stdenv.lib.platforms.mesaPlatforms;
   };
 }