Someone correct me if I'm wrong.
That's Jag right? In any event, since the key doesn't seem to have any associated account or URL, I wouldn't worry TOO much. I am curious why it won't delete though...
The keychains file is kept in ~/Library/Keychains/{username} but it's in some kind of database format (duh!) so if someone knows the format and can play with it... Each key is contained in this file (i.e, they're not all separate files).