remove :includes => :quiz_submission

fixes CNVS-9933

test plan:
 - basic regression on the following:
   - teacher activity pages
   - gradebook pages
   - grades page
   - gradebook upload
   - changing due dates on assignments
   - submissions api
   - assignments api
 - sorry

Change-Id: I7bb4c32a74b159565772da8ee1d5a43e27369ca0
Reviewed-on: https://gerrit.instructure.com/30367
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>