updated how generator check for distance map data.

Updated test for generators to check that distance map is not recomputed when loaded correctly
fixed formatting and removed debug prints

flatland/envs/observations.py

@@ -64,7 +64,6 @@ class TreeObsForRailEnv(ObservationBuilder):
 
     def _compute_distance_map(self):
         agents = self.env.agents
-        print("Computing distance map")
         # For testing only --> To assert if a distance map need to be recomputed.
         self.distance_map_computed = True
         nb_agents = len(agents)