Historically, the CourseEnrollment model used to have a `course_id`
field. A lot of tests still call the factory using that. Instead of a
`course_id` field this model now has a `course` field which is a foreign
key to the CourseOverview model.
The factory still accepts the course_id but uses it to create the
relevant CourseOverview object where necessary. This commit fixes two
issues with the factory.
1. If the course id is passed in as`course_id` instead of `course__id`
then, the generated CourseOverview does not have the correct course_id.
2. Even though the CourseEnrollment model no longer needs the
`course_id` parameter, we were still passing it through. We now remove
it so that it is not passed through to the CourseEnrollment model
instantiation.
3c618ad04d