Fix ROOT-5284 which was due to a unusual setup (in TParallelCoord) leading to only partial cleanup.

In some case, for example TParallelCoord, a list (the pad's list of
primitives) will contain both the container and the containees (the
TParallelCoorVar) but if the Clear is being called from the destructor
of the container of this list, one of the first thing done will be the
remove the container (the pad) for the list (of Primitives of the
canvas) that was connecting it (indirectly) to the list of cleanups.

So in Clear and Delete, we temporarily add each list and TObjArray to
the cleanup list and remove it later.