Since this is database work a programmer or super super user would need to know how to do, you would need to announce in a news forum or some such that the files are no longer available. I'm guessing that the links would no longer exist.
As we have requirements here in the US to preserve these records, we don't actually anticipate removing them until 2 or so years after the course has ended. At which point we archive the course and only go back to it as needed, which, so far has been, essentially never.
Storage being so cheap now, I'm wondering if you really need to delete them.