the VirtualDevice is a SvpSalVirtualDevice and it
uses its own SvpSalGraphics to render to itself,
so we don't have to worry about being asked to
render to a VirtualDevice

i.e. Revert "just in case, fallback if not cairo-surface"

This reverts commit 756b2c94.

Conflicts:
	vcl/unx/gtk3/gdi/gtk3salnativewidgets-gtk.cxx

Change-Id: I3bd3ce42e7c943f8cfca1cc1d2ea6e5eb51bb349