writers.writePython2 and writePython3: use "bare" python if no deps are needed

`python.withPackages` has a runtime dependecy on bash since it's wrapped with
`makeWrapper`. This fix avoids bash as runtime dependency when it's not
needed.

as discussed here: https://github.com/NixOS/nixpkgs/issues/93609#issuecomment-662880047

pkgs/build-support/writers/test.nix

@@ -152,6 +152,14 @@ let
       """)
       print(y[0]['test'])
     '';
+
+    python2NoLibs = writePython2 "test_python2_no_libs" {} ''
+      print("success")
+    '';
+
+    python3NoLibs = writePython3 "test_python3_no_libs" {} ''
+      print("success")
+    '';
   };