TNL-281: reduce amount of JS in marketing iframe

It probably makes sense to not send lms-main_vendor.js for this view since it's 1MB and dramatically slows down the first page render. 

iframe itself: https://courses.edx.org/mktg/edX/DemoX.1/2014
page: https://www.edx.org/course/edx/edx-demox-1-demox-4116

Acceptance criteria:

  * Allow the bit of LMS that displays the registration button on the marketing site to load without the whole LMS javascript coming along with it.