Previously, we'd been avoiding PLS due dates for ORA *sections*.
That is, if a section had only ORA content, we'd not set a PLS
due date for anything in that section.
If any content in that section had non-ORA graded content however,
we would set dates on all subsections, including the ORA one.
This resulted in some ORA-only subsections showing up twice on the
dates tab. So this patch simply brings down the ORA-only check
to a *subsection* level, not a section one.
