NEW YORK — Six people were shot, one fatally, as a fight between rival teens spiraled out of control in a Bronx subway station on Monday, according to police. Dozens of people were on the northbound No. 4 platform at the elevated Mount Eden Ave. station on Jerome Ave. near Mount Eden Ave. when a train rolled in around 4:35 p.m., authorities said. Inside the train, two groups of teenagers were fighting. When the doors opened, at least one of the people involved in the argument took out a gun and fired shots, NYPD Chief of Transit Michael Kemper said at a Monday night press conference. As people…