It depends on the extent of the shaking. Generally I'd say it's a myth because you can practice the shaking away, giving you more stability and dexterity. If the underlying cause is neurological and you experience a lot of tremors that you know won't go away it's not recommendable however. I believe you could still become a surgeon though, if you specialise in urology for example and learn how to perform robotic surgery (it's becoming more and more standard in developed countries) since there are settings deciding how much movement will trigger the robotic arm, but even so you probably wouldn't be allowed to do that without having hands on training before and now I'm just speculating since I don't really know :D