Remove addding nixpkgs (did not fix the issue)

panel/default.nix

@@ -22,7 +22,6 @@ in
     packages = [
       pkgs.npins
       manage
-      pkgs.nix
     ];
     env = {
       NPINS_DIRECTORY = toString ../npins;

panel/nix/configuration.nix

@@ -37,7 +37,6 @@ let
       django-libsass
       django_4
       setuptools
-      pkgs.nix
     ]
     ++ cfg.package.propagatedBuildInputs
   );

panel/nix/package.nix

@@ -2,7 +2,6 @@
   lib,
   sqlite,
   python3,
-  nix,
 }:
 let
   src =
@@ -51,7 +50,6 @@ python3.pkgs.buildPythonPackage {
     in
     [
       sqlite
-      nix
     ]
     ++ pythonPackages;