`_id.course` doesn't have the `course_id` (which is, ordinarily, `org/course/run`), it just has the `course` part of that id. That means that this search will a) find courses from other organizations, and b) find content from other runs. Given our current id structure, the latter is unavoidable (with this style of query), but the former should be restricted.

A better approach, given the `_id` structure of the mongo backend, would be to walk the `children` pointers to find all of the content that needs to be deleted.