Preservation Chicago’s annual list of the seven most endangered buildings is so big that this year it includes eight historic sites. Topping the list, issued Wednesday, is an urgent late addition: two century-old, early Chicago skyscrapers that the federal government purchased 15 years ago and now wants to demolish. A $52 million bill is moving through Congress that would tear down the Century and Consumers buildings in the 200 block of South State Street, long-vacant monuments to early Chicago high-rise architecture. The government acquired the buildings in 2007 as a security buffer and poten…