optimize user_access_report query

fixes CNVS-11007

test plan
 - specs should pass

Change-Id: I9acf26fc857096c172f5f2467fba29e895041758
Reviewed-on: https://gerrit.instructure.com/29755
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>