drop ReviewActionReasons support in reviewer tools, and cinder_policy_review_reasons switch

[eviljeff]

Fixes: mozilla/addons#16121

Description

Removes support for ReviewActionReason in the reviewer tools, and the cinder_policy_review_reasons waffle switch.

Context

There's a lot of old code removed, but also a fair number of reviewer tests were only testing with reasons so needed updating.

Apparently auto_reject only took into account reviewer action reasons too...

I retained support in admin and models for historic reference, and that it's still used in the blocklist admin - follow-up would be to strip out functionality that is unused for blocklist admin - or just remove it entirely as manual blocklist submissions will become more and more rare going forward.

The reviewer tools reply action was using reviewactionreaons (for the canned responses), irregardless of the waffle switch, but switching it to use Cinder Policies didn't make much sense - reply is used when we're not enforcing a policy. So I just removed support.

Testing

Approve/Reject some add-ons in the reviewer tools and check everything works as expected.

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[eviljeff]

This is a drive-by fix - Andreas mentioned on Slack that policies with this enforcement action weren't showing up.