BOSTON — A federal judge on Tuesday gave federal prosecutors until Sept. 10 to decide if they will seek the death penalty against Louis D. Coleman III, the Providence man accused of abducting a woman outside a Boston nightclub whose body was found in his trunk. “If it’s not going to be a death-penalty case, we shouldn’t litigate it like one,” U.S. District Court Chief Judge Frank Dennis Saylor IV said in a remote conference with federal prosecutors and the defense team for Coleman. The deadline comes as Attorney General Merrick B. Garland issued a memorandum July 1 imposing a moratorium on federal executions while a review of the Justice Department’s policies and procedures is pending.