it doesn't have to be media or bootlegs...
"Counterfeits, unauthorized replicas, unauthorized items (such as counterfeit watches, handbags, or other accessories) or unauthorized copies (such as copies of software programs, video games, music albums, movies, television programs, or photographs) are not permitted on eBay."
i would say that this falls into the category of an unauthorized item... it has the nintendo company logo and they did not create or endorse the item. it is also an unauthorized copy, as you are not the artwork's creator and the creator did not give you permission to use the artwork for profit.
justify it all you want, man... it's a violation of ebay rules. and removing the insert from you auctions helps, but it doesn't ignore the fact that you did this in the first place, knowing that you'd be making easy money by selling something that really wasn't yours.