A layer's bounds leave out its hidden objects and a clipping container's
are its clipping path's, so objects beyond the canvas inside them were
kept. Layers and groups are now looked into object by object.
A clipping path beyond the canvas goes with the objects it clips, so no
other object becomes the clip; a top-level clipping layer is emptied and
stops clipping. A removed artboard's ruler origin goes and its id is
retired, as deleting it does.