Only if the materials are not being referred to elsewhere. I would take them out by moving the directories, check any course that might use the materials and if it is all good, then delete.
However, in education, if you stand still long enough, they will catch up to you... I would archive rather than delete, even if the archive is off the Moodle server, or to a hard disc stored elsewhere. All networks should have a data store, which contains stuff going back decades in some cases, The issue is that the technologies change so rapidly, that they can date to the point where there is no equipment left to access the data. For the most glaring example of this was last week when I saw someone finally tossed out 3.5 and 5.25 inch floppy discs that had been in the store room. We do not have any floppy disc readers anywhere in the network, but we still had the discs, so I hope they haven't tossed out anything important without it being on CD, DVD or BluRay somewhere, even a tape... Wonder what will happen when usb will no longer support v1 devices? Or CDs can no longer be read... be a while but will happen I expect.