Clean up after track selection experiment

This cleans up the code left over from the track selection experiment ([ECOM-16](https://openedx.atlassian.net/browse/ECOM-16)). These changes don't include cleanup of the SCSS used to style the `choose`, `_verification_header`, and `_verification_support` templates; that seemed like a separate story, and UX is out today.

@wedaly and @stephensanchez, could you review this?
This might be bad for the following scenario, if I understand it correctly.
1) User registers for course, and gets the options (honor, verified)
2) User chooses honor, un enrolls via dashboard.
3) User changes mind, goes to register for course
4) Course has an inactive enrollment for course, gets redirected to dashboard?