pythonPackages.pygobject{,3}: let python.buildEnv detect it

pkgs/development/python-modules/pygobject/3.nix

@@ -13,6 +13,8 @@ stdenv.mkDerivation rec {
   buildInputs = [ python pkgconfig glib gobjectIntrospection ];
   propagatedBuildInputs = [ pycairo cairo ];
 
+  passthru.pythonPath = [];
+
   meta = {
     homepage = http://live.gnome.org/PyGObject;
     description = "Python bindings for Glib";

pkgs/development/python-modules/pygobject/default.nix

@@ -20,6 +20,8 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ python pkgconfig glib ];
 
+  passthru.pythonPath = [];
+
   # in a "normal" setup, pygobject and pygtk are installed into the
   # same site-packages: we need a pth file for both. pygtk.py would be
   # used to select a specific version, in our setup it should have no