Add the activate account step to the verified workflow.

* Changing approach such that email activation is not a step.
* Removing stale line of code.

@wedaly @dianakhuang @rlucioni 
This data attribute is already present on the page, at [line 52](https://github.com/edx/edx-platform/blob/sanchez/add-activate-account/lms/templates/verify_student/pay_and_verify.html#L52).