If you just want the lock off, there's one bolt holding it on. The other side is a locating pin. The bolt is like a hex head, but they rounded it out. A normal hex key will slip if you try to use one.
I got mine off using vice grips. Put the side of the jaws flush with the plate and clamp down on the bolt head. Give it a little push. If it slips, reclamp it. Keep doing this and it will wear the nut oblong until it can get a good grip. My lock was a little loose, so it was pretty easy for me. The bolt was already broke free.
I replaced the bolt with a stainless steel security hex head (the kind with the peg in the middle). The bolt came from a set for attaching license plates that i got at Autozone for under $2. It came with the security hex key. I just had to cut it the right length. I added some blue loctite to make sure it didn't rattle loose.
You could also try to cut a groove through the head with a dremel. Then use a wide, flat headed screwdriver to give it a twist. This way would be easier with the tire off.