A firearms and tactics instructor must keep his personal views to himself when he offers his professional opinions as an expert witness for two Chicago police officers who shot a man to death, a federal judge held.In a written opinion, U.S. Magistrate Judge Jeffrey I. Cummings of the Northern District of Illinois denied a motion by Darius Cole-Garrit’s mother to bar the expert from taking the witness stand in the trial of her excessive force lawsuit against the officers and the city of Chicago.But Cummings held Emanuel …