Update CoursesWikis data migration task to use Assignments
Update CoursesWikis data migration task to use Assignments

This matches the way we previously imported revisions for courses; the wiki_ids feature was an edge case that didn't reflect the intention.

WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard