we need to update the tutorial to remove the outdated functions such as read_zones(network)

[asu-trans-ai-lab]

I believe that ve we do not need zone.csv so the function is not needed. We read zone_id only from field zone_id in file node.csv pg.read_zones(network)

https://github.com/jdlph/Path4GMNS/blob/dev/tutorial/tutorial.ipynb