remove grants_rights? and cached_context_grants_rights?

refs: CNVS-11425
refs: CNVS-11197

Change-Id: I9df4d3c408be0a1aede6cc987a982b5e2f688ce0
Reviewed-on: https://gerrit.instructure.com/35829
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>