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/tools/misc/swig/2.x.nix

@@ -45,6 +45,6 @@ stdenv.mkDerivation rec {
 
     platforms = lib.platforms.linux ++ lib.platforms.darwin;
 
-    maintainers = [ lib.maintainers.urkud ];
+    maintainers = [ ];
   };
 }

pkgs/development/tools/misc/swig/3.x.nix

@@ -31,6 +31,6 @@ stdenv.mkDerivation rec {
     # Different types of licenses available: http://www.swig.org/Release/LICENSE .
     license = licenses.gpl3Plus;
     platforms = with platforms; linux ++ darwin;
-    maintainers = with maintainers; [ urkud wkennington ];
+    maintainers = with maintainers; [ wkennington ];
   };
 }