Fighters with a Kurdish separatist militant group that has waged a decades-long insurgency in Turkey began laying down their weapons in a symbolic ceremony on Friday in northern Iraq, the first concrete step toward a promised disarmament as part of a peace process. The Kurdistan Workers’ Party, or PKK, announced in May that it would disband and renounce armed conflict, ending four decades of hostilities. The move came after PKK leader Abdullah Öcalan, who has been imprisoned on an island near Istanbul since 1999, urged his group in February to convene a congress, and formally disband and disarm.