cosmic-applibrary: remove unnecessary patch

This patch currently does nothing, so we can remove it

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

···
     "target/${stdenv.hostPlatform.rust.cargoShortTarget}"
   ];
 
-  postPatch = ''
-    substituteInPlace justfile --replace '#!/usr/bin/env' "#!$(command -v env)"
-  '';
-
   passthru = {
     tests = {
       inherit (nixosTests)