Looks like corner_arrow is the only asset that's still being used in the codebase, and that's being pulled from AWS.

It looks like the other three assets aren't hosted on AWS, but they're also no longer used... so they should be safe to delete.

As an aside, even though these assets are preserved in the git history--it'd probably be good to have a Dropbox or Google Drive or whatever to hold onto them for archival purposes/in case they happen to be relevant in the future. (cc @ashoat)