By Kay Johnson KABUL (Reuters) - The U.S.-led coalition in Afghanistan formally ended its combat mission on Sunday, more than 13 years after an international alliance ousted the Taliban government for sheltering the planners of the Sept. 11, 2001 attacks on American cities. About 13,000 foreign troops, mostly Americans, will remain in the country under a new, two-year mission named "Resolute Support" that will continue the coalition's training of Afghan security forces. The Afghan army and police are struggling to fight against Taliban militants who this year killed record numbers of Afghans. ...