Printing the slice information makes sense for Init Plans, which are
dispatched separately, before the main query. But not so much for other
Sub Plans, which are just part of the plan tree; there is no dispatching
or motion involved at such SubPlans. The SubPlan might *contain* Motions,
but we print the slice information for those Motions separately. The slice
information was always just the same as the parent node's, which adds no
information, and can be misleading if it makes the reader think that there
is inter-node communication involved in such SubPlans.