mehmet oz is on staff at columbia 's college of physicians and surgeons .
dr oz is the vice chairman and professor of surgery at the medical school .
group of ten top doctors sent letter to school urging for oz 's dismissal .
said there 's no scientific proof his ` miracle ' weight-loss supplements work .
columbia said it ` is committed to the principle of academic freedom '
university has not removed tv celebrity doctor from his faculty position .