City officials have cleared out homeless pavement dwellers from the area around the United Nations headquarters in preparation for the high-level General Assembly session starting Monday, keeping them out of view of the visiting leaders and raising the security level. The dozens of homeless people, who live under tarps, cardboard boxes, umbrellas and construction sheds for most of the year along First Avenue, where the UN is located, and Second Avenue and the side streets in the area, were out by Sunday evening.