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