python: Use packages from previous stage in setup-hooks

This makes sense as these are tools we want to run at build time.

pkgs/development/interpreters/python/hooks/default.nix

@@ -1,7 +1,6 @@
 # Hooks for building Python packages.
 { python
 , lib
-, callPackage
 , makeSetupHook
 , disabledIf
 , isPy3k
@@ -9,6 +8,7 @@
 }:
 
 let
+  callPackage = python.pythonForBuild.pkgs.callPackage;
   pythonInterpreter = python.pythonForBuild.interpreter;
   pythonSitePackages = python.sitePackages;
   pythonCheckInterpreter = python.interpreter;