It is definitely illegal, but there's nothing stopping anyone from doing it. I'm not saying people should do that, just that they can and do, with little negative effects.

I also acknowledge that handing control to a modified computer is a little different than manually controlling a modified car, and it could have much more disastrous effects. But I don't think anyone will actually do that.

(As for when I did drive without brakes that one time, my car had a manual transmission and a fully-functioning hand brake, and I was in full control of the vehicle at all times. I drove slowly and carefully along back roads, and kept a 100 m gap ahead of me at all times. I was well-practiced at down-shifting to slow down, and used to regularly come to a complete stop from freeway speeds down the ramp without touching the brake pedal, just because I could. And "no brakes" is a slight exaggeration; I had some brakes, but there was a leak and I didn't want to use them unless I absolutely had to, and I didn't have to. Would I do it again? Probably not, but I was young and willing to take minor risks like that.)