Remove Item.window

Remove Item.window

Window is a type in a different import, so we can't just casually use
it in Item. Note that this API was going to be new in the next release,
so it can be safely removed (at least until we do it right).

Change-Id: I9e3eb5f65ea5f46d30fb7905d0f9c479daaccbff
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>