Delete loose edges left behind by sculpting with collapse-short-edges

After deleting a face, check for unused edges and delete them.

Fixes bug [#33891]
projects.blender.org/tracker/?func=detail&aid=33891&group_id=9&atid=498

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53915 954f8c5b-7b00-dc11-b283-0030488c597c