In preparation for switching to handling the output shape purely by what we
paint, stop applying a shape to the frame of the window. Even when we restore
handling the output shape, this will change the behavior with respect to input;
transparent areas between the frame and the contents will stop clicks rather
than passing them through, but that is arguably at least as expected
considering how that we decorate shaped windows with a frame all around.

https://bugzilla.gnome.org/show_bug.cgi?id=644930