NEW YORK — A 16-year-old boy was taken into custody Thursday for the Bronx subway station gang shooting that left a bystander dead and five others wounded, police said. The teen was grabbed up after he was identified as one of at three wanted suspected triggermen in the Monday afternoon rush hour shooting at the Mount Eden subway stop Monday afternoon. No charges were immediately filed. A “chance encounter” between rival gangs sparked a fight, during which three men pulled their guns and started blasting, cop said. The suspects continued firing at their rivals on the train platform and on the …