It was a somber scene outside New York’s City Hall on Wednesday afternoon. Four coffins sat at the foot of the steps; one by one, taxi drivers covered them with white flowers, before assembling on the steps and shouting for the city to “stop Uber’s greed” and “stop making us slaves.” It was the second such gathering in two months, as drivers and their advocates mourned another suicide that they attribute to the rise of ride-hailing services like Uber and Lyft.