At Mark Hammond's request, removing registry key

Software\Python\PythonCore\2.0\Dll\Python20.dll -- it's no longer
needed according to him.

Note: not yet tested!

PCbuild/python20.wse

@@ -995,11 +995,6 @@ item: Edit Registry
   New Value=%MAINDIR%\Lib\plat-win;%MAINDIR%\Lib;%MAINDIR%\DLLs;%MAINDIR%\Lib\lib-tk
   Root=2
 end
-item: Edit Registry
-  Key=Software\Python\PythonCore\%PY_VERSION%\Dll
-  New Value=%_DLLDEST_%\Python20.dll
-  Root=2
-end
 item: Edit Registry
   Key=Software\Python\PythonCore\%PY_VERSION%\Modules
   Root=2