treewide: remove wkennington as maintainer

He prefers to contribute to his own nixpkgs fork triton.
Since he is still marked as maintainer in many packages
this leaves the wrong impression he still maintains those.

pkgs/development/libraries/msgpack/generic.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
     description = "MessagePack implementation for C and C++";
     homepage    = https://msgpack.org;
     license     = licenses.asl20;
-    maintainers = with maintainers; [ redbaron wkennington ];
+    maintainers = with maintainers; [ redbaron ];
     platforms   = platforms.all;
   };
 }