OSHKOSH, Wis.—A man serving two life terms for killing a Wisconsin couple in a slaying that went unsolved for decades has died in prison, state corrections officials confirmed. Raymand Vannieuwenhoven, 85, was convicted last year of fatally shooting 25-year-old David Schuldes and 24-year-old Ellen Matheys in a Marinette County park on July 9, 1976, in…