William S. Dietrich II, a longtime steel executive who pledged gifts to the University of Pittsburgh and Carnegie Mellon University last month totaling $390 million, has died. He was 73, the Associated Press reports. Dietrich’s death was announced Friday by the John A. Freyvogel Funeral Home. It said he died Thursday. Carnegie Mellon said the cause was complications from cancer. A $265 million gift to Carnegie Mellon, announced Sept. 7, was one of the largest in recent years from an individual to a private university, and the largest in the school’s history…