With my multi sort PR I changed the sort property on saved searches to contain a nested array. Discover and Dashboard were backwards compatible with the old format but it turns out the nested array caused issues for CSV export. Instead of trying to support single and two dimension arrays everywhere, this PR simply adds a migration for saved searches in 7.4 and updates our sample data sets so that we can always expect sort objects to be two dimensional arrays. I also cleaned up the backwards compatibility code in Discover and Dashboard.