“I wish you success in your job interview.”

Personally, I don’t think “good luck” implies that the person can’t make it on his own. I think it’s just a wish for that extra little push of fate: the interviewer is in a good mood; the job seeker did a final mirror check and noticed the poppyseed between his teeth.

But if you don’t like it, naturally, you should not say it.

In fact, you could even call attention to it.

“I would wish you good luck if I didn’t know that you already have everything you need to ace that job interview tomorrow.”