SPOKANE — Randy Dorn is stepping down after eight years as state superintendent of public instruction, and two Democrats are vying to replace him as head of Washington’s K-12 public education system. The nonpartisan job pays $132,000 a year and oversees some $9 billion in education spending. State Rep. Chris Reykdal, 44, of Tumwater, has served three terms in the state House and is an administrator for the Washington State Board for Community and Technical Colleges.