treewide: remove the-kenny from maintainers

@the-kenny did a good job in the past and is set as maintainer in many package,
however since 2017-2018 he stopped contributing. To create less confusion
in pull requests when people try to request his feedback, I removed him as
maintainer from all packages.

pkgs/applications/misc/curaengine/stable.nix

@@ -25,6 +25,5 @@ stdenv.mkDerivation {
     homepage = "https://github.com/Ultimaker/CuraEngine";
     license = licenses.agpl3;
     platforms = platforms.linux;
-    maintainers = with stdenv.lib.maintainers; [ the-kenny ];
   };
 }