I've never done it......BUT, if it it's spot welded, you should be able to drill out the spot welds. Once they are gone, they should fall right off unless the ceramic coating is holding them together after that. Even then, you should be able to just wiggle them and break them off.
What do you have going on? If you need a kettle for a project, I have a black daisy wheel kettle I'd offer up before you start grinding off tabs on a performer kettle. I'd hate to see a performer kettle killed if it's still usable.