Use one of these and cut off the head, remove the brace then cut the bolt off. Just be careful of sparks, so put some cardboard or other material to protect the surrounding area.
Unless you (or a friend) have one already, I bought this one from Harbor Freight and works great. You will be amazed how many uses you will get out of this cheap tool.
https://www.harborfreight.com/3-in-h...ool-63023.html