Remove unused JavaScript variables.

Summary: There are a bunch of unused variables in JavaScript files. These were identified with JSHint.

Test Plan: It's pretty hard to test this thoroughly... on inspection, it seems that everything //should// be okay (unless we are doing weird things with the JavaScript).

Reviewers: chad, #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9676