You are right, the interface changed it seems but the documentation was not updated (feel free to open an issue here Issues · PX4/PX4-user_guide · GitHub)
PX4 retrieves the GPS location direclty from Gazebo now, and the GPS origin is set in the world file:
PX4-gazebo-models/worlds/default.sdf at 6b4ed09d1b495fbff663f098979cc046df013abd · PX4/PX4-gazebo-models · GitHub
