outdated course instances should go away

[kohlhase]

This is the first switchover, and I see that the old GenCS I course still is in my "Instructor in:" view on my course managment pane. It would be good if that went away (into a "more" link at the bottom).
If I remember correctly, we wanted to specify the semester of the course in the course page (but I do not remember filling that out in the new course instance page) and that information can be used to make this behavior.