Remove unused internal property in OrbitPlotter
Remove unused internal property in OrbitPlotter

This was the one giving warnings in MyPy!

Juanlu001/poliastro,newlawrence/poliastro,anhiga/poliastro,anhiga/poliastro,newlawrence/poliastro,anhiga/poliastro,poliastro/poliastro,Juanlu001/poliastro,newlawrence/poliastro,Juanlu001/poliastro