Don't show course about page link when we have the marketing site.

STUD-733

@chrisndodge Can you review? There is currently no way for us to know what the about page URL will be on the Drupal site. Karen had set up redirects for courses running last semester, but there is no plan to do this going forward. And also, the about page isn't visible on the marketing site while the course is still under development.

To reduce course team confusion, removing the advertising of the about page URL until we have the API to communicate with Drupal.