move default.nix to shell.nix

python_environment/default.nix

@@ -1,20 +0,0 @@
-with import <nixpkgs> {};
-
-stdenv.mkDerivation {
-  name = "myPythonEnv";
-  buildInputs = with pkgs; [
-    python3Full
-    python3Packages.virtualenv
-  ];
-  src = null;
-  shellHook = ''
-    if [ ! -d .venv ]; then
-      python -m venv .venv
-    fi
-    source .venv/bin/activate
-    pip install --upgrade pip
-    if [ -s requirements.txt ]; then
-      pip install -r requirements.txt
-    fi
-  '';
-}