window-group: Don't special-case the unredirected window

Since the unredirected window MetaWindowActor is stacked on top, it
will naturally get culled out of the process, so we can remove the
special casing here. Unfortunately, with the way that the code is
currently structured, it's too difficult to actually prevent setting
the clip / visible regions if the window is redirected, so just let
those be set for unredirected windows for now.