It's cleaner to let the apps do this themselves than exposing their
underlying vcl::Window.

(cherry picked from commit bfd79be4)

Conflicts:
	sc/inc/docuno.hxx
	sd/source/ui/inc/unomodel.hxx
	sw/inc/unotxdoc.hxx

Change-Id: Iff2442dd325fa65a0cf3ad4aa7f918542dab1e4c