Setting map map's yaml path to empty string, since overridden in laun…

…ch (#3123)

* Update nav2_params.yaml

* Update nav2_params.yaml

* Update nav2_params.yaml

nav2_bringup/params/nav2_params.yaml

@@ -257,7 +257,9 @@ global_costmap:
 map_server:
   ros__parameters:
     use_sim_time: True
-    yaml_filename: "turtlebot3_world.yaml"
+    # Overridden in launch by the "map" launch configuration or provided default value.
+    # To use in yaml, remove the default "map" value in the tb3_simulation_launch.py file & provide full path to map below.
+    yaml_filename: ""
 
 map_saver:
   ros__parameters: