Clear notifications about commits when viewing them

Summary: We were missing this option on the response, so notifications about commits (e.g., tokens given) don't clear when viewing the commit.

Test Plan: Gave a commit a token with user A, viewed notification with user B, viewed commit with user B and verified notification cleared.

Reviewers: garoevans, btrahan

Reviewed By: garoevans

CC: aran

Differential Revision: https://secure.phabricator.com/D6041