Closing as a duplicate should use "closed" iconography

Summary: Uses the check icon for closed, which is the primary action taken.

Test Plan:
Close as a duplicate, seen new icon.

{F236048}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10882