writerfilter: remove unused qname attribute

Change-Id: I412390fba4caa4579dec0dab68f4a1c276284118
DOCX export: prevent multiple paragraphs in some SDT containers

E.g. Word doesn't do anything if you hit return in the middle of a
title; if that's so, then we should handle this situation on export as
well.

Change-Id: Ib5b52a59250b09c97023b53906b8046f530d0e31