A Royal Oak doctor who headed a medical marijuana clinic was ordered Friday to stand trial on charges he threatened to kill the county prosecutor, a retired judge and others.Dr. Kumar A. Singh, 47, appeared with defense attorney Paul Stablein before Royal Oak 44th District Judge Jamie Wittenberg for a preliminary examination where prosecutors were prepared to present witnesses, but Singh indicated through his attorney he wanted to waive his right to the hearing and pursue his case in Oakland County Circuit Court trial court.