Update config to not rely on Khan

Test Plan:
- Load config from a page that doesnt load khan-exercises, dont see error about Kahn being undefined
  (which is possible in pf-article-latex branch, in incognito mode, on an article with <code class="latex">)

Reviewers: alpert

Reviewed By: alpert

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D6201