Don't eta-expand unsaturated primops
Previously, as described in Note [Primop wrappers], hasNoBinding would
return False in the case of PrimOpIds. This would result in eta
expansion of unsaturated primop applications during CorePrep. Not only
did this expansion result in unnecessary allocations, but it also meant
lead to rather nasty inconsistencies between the CAFfy-ness
determinations made by TidyPgm and CorePrep.
This fixes Trac #16846.