get rid of count(*) overrides query

refs CNVS-6763

Test plan:
  basic overrides regression test

Change-Id: I0874db750299709345b241c197a0973e31569cc5
Reviewed-on: https://gerrit.instructure.com/28799
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Liz Abinante <labinante@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>