Cops have released surveillance images of a heartless goon who they say pummeled a 10-year-old girl and her mom onboard a Bronx train last month, authorities said. The mother and daughter were standing onboard a northbound No. 5 train at the Simpson Avenue station, near Westchester Avenue, just after 4:30 p.m. Oct. 18 when a woman approached them and started punching both in the face and mouth, police said. The motive for the assault remained unclear Friday. The suspect got off the train after the attack, cops said. The mother and daughter were taken to Jacobi Medical Center in stable...