cortex: Remove package

I removed cortex it is rather unmaintained. The last update (as of
writing) was 8 months ago, there was no release ever.

For a better alternative, have a look at `rtv`.

pkgs/applications/misc/cortex/default.nix

···
-{ stdenv, fetchgit, python3 }:
-
-stdenv.mkDerivation {
-  name = "cortex-2015-08-23";
-
-  src = fetchgit {
-    url = "https://github.com/gglucas/cortex";
-    rev = "ff10ff860479fe2f50590c0f8fcfc6dc34446639";
-    sha256 = "0pa2kkkcnmf56d5d5kknv0gfahddym75xripd4kgszaj6hsib3zg";
-  };
-
-  buildInputs = [ stdenv python3 ];
-
-  prePatch = ''
-    substituteInPlace cortex --replace "/usr/bin/env python3" "${python3}/bin/python3"
-  '';
-
-  installPhase = ''
-    mkdir -p $out/bin
-    cp cortex $out/bin/
-    chmod +x $out/bin/cortex
-  '';
-
-  meta = with stdenv.lib; {
-    homepage = "http://cortex.glacicle.org";
-    description = "An ncurses reddit browser and monitor";
-    license = licenses.mit;
-    maintainers = with maintainers; [ matthiasbeyer ];
-    platforms = with platforms; unix;
-  };
-
-}

pkgs/top-level/all-packages.nix

···
     inherit (gnome2) libgnomeui GConf;
   };
 
-  cortex = callPackage ../applications/misc/cortex { };
-
   csound = callPackage ../applications/audio/csound { };
 
   cinepaint = callPackage ../applications/graphics/cinepaint {