Updated RigidBodySystem to not use deprecated addRobotFromSDF() method.
Updated RigidBodySystem to not use deprecated addRobotFromSDF() method.

sheim/drake,billhoffman/drake,billhoffman/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,sheim/drake