keep quiz stats in beta only for now

closes CNVS-14001

test plan:

  - quiz stats feature should be available in beta
  - quiz stats feature should not be available in prod

Change-Id: If094589558b44b11b989b0b0e38b36359a1edfb3
Reviewed-on: https://gerrit.instructure.com/37347
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>