I'd like an answer to this as well. Every once in a while I'll forget to enable the "replace drawing" function when I submit a replacement drawing and it really bothers me seeing both of them in my personal diagram. I remember illustrators used to be able to delete their own drawings but that option has since been removed for whatever reason.
In any case, here are some drawings I've already replaced that I would like deleted
http://skyscraperpage.com/edit/drawing/?81791
http://skyscraperpage.com/edit/drawing/?76510
It would be greatly appreciated if someone would delete them for me!