refactor content_item methods

test plan
 - specs should pass

Change-Id: I0e5253ba139913d533ab87a75ec897e9ad4e1e0c
Reviewed-on: https://gerrit.instructure.com/42923
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nathan Mills <nathanm@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Bracken Mosbacker <bracken@instructure.com>