The solution does not work for Events.
I have this problem every time I update a course.
I have seen it posted many times and the Canvas employees answering do not seem to understand the real question.
Deleting or changing dates for assignments and to-do list items is easy.
Deleting old Events from an imported course's "Course Summary" list is impossible.
Please fix this.
Nobody wants last year's events to show up on this year's syllabus.
The only work-around I know of is to manually delete events from the old course before importing.
Then start over. You can lose a lot of work this way.