Get rid of an html-style comment in javascript.

Summary:
Could use //, but the comment is not adding anything new, that I can
see, so I'm happy to just nix it.

This was messing up the python javascript parser I was throwing at
this file.

Test Plan: None

Reviewers: eater, alpert

Reviewed By: alpert

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D2103