For more than a year, Don Shelby has made no secret about the fact that he plans to retire when his contract expires on Dec. 31. That vow will be official Wednesday morning when WCCO's veteran news anchor holds a press conference at the TV studio. Shelby, who joined the CBS affiliate in 1978 and began co-anchoring the 10 p.m. broadcast in 1985, is expected to spell out details on when he'll officially step down. His successor is expected to be named at the conference.