Clear "X awarded a token to event Y" stories when visiting event page

Summary: These detail pages don't have a "pageObjects" configuration, so we don't clear, e.g., token stories correctly when users load them.

Test Plan: Will clear a token story in production.

Reviewers: btrahan, lpriestley, chad

Reviewed By: chad

Subscribers: chad, epriestley

Differential Revision: https://secure.phabricator.com/D13582