cosmic-player: remove unneeded patch

It doesn't do anything, so removed it

pkgs/by-name/co/cosmic-player/package.nix

···
 
   cargoHash = "sha256-DodFIfthiGFSvXWfPsPjFhNY6G7z3lb6pfc5HtUXhMo=";
 
-  postPatch = ''
-    substituteInPlace justfile --replace-fail '#!/usr/bin/env' "#!$(command -v env)"
-  '';
-
   nativeBuildInputs = [
     just
     pkg-config