re-enable deleted rubrics on import

test plan:
* create a course with a rubric
* copy the course into another course
* delete the copied rubric
* recopy the original course into the copied course
* the rubric should be available again

fixes #CNVS-12958

Change-Id: Ic8ddb8b9c629d8d27baea9f1a08db60c7d8317d0
Reviewed-on: https://gerrit.instructure.com/34728
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>