Turn on any cable news channel and you’re bound to hear one talking head or another droning on about the nation’s health care crisis. Rarely, however, do you hear it from the prospective of a doctor in the trenches. And not just any doctor, but a doctor who is a product of the urban community that he serves. That’s what you get from the book “Living and Dying in Brick City: An E.R. Doctor Returns Home.” The author, Dr. Sampson Davis, is an emergency room physician in a Newark hospital, and sometimes the patients who come through its doors are a reminder of the road he didn’t take.