A ball of fire, a plume of smoke and almost all of Gotham General Hospital was gone. A wave of heat swept over about 150 people who had camped out at the corner of Cicero Avenue and Ferdinand Street to watch the pyrotechnics go off for a scene in the upcoming “Batman” sequel, “The Dark Knight.”Hollywood came to the West Side Wednesday afternoon to blow up the five-story administration building that Brach’s Candy abandoned with the rest of its sprawling complex in 2003.