make evaluate_for_course arguments required

fixes CNVS-12343

test plan:
alerts for a course should still get sent

Change-Id: I149f72e5604c3d83a6a4aa63f2adcea5325ae9f5
Reviewed-on: https://gerrit.instructure.com/33220
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>