I don't think you can make people stop asking.

You could answer with 'I'm not sure,' or 'I'm just seeing where this takes me,' or something equally vague, and then immediately deflect with a question of your own.

I ask people what they want to do with X and it's not because I want them to fail. It's because it's a conversation starter -- if I am sitting in a class with someone and want to meet new people, I have to say something - and the class or program is what we have in common.