refactor(planning_launch): remove duplicated lane change parameter (#328)

Author: purewater0901

autoware_launch/config/planning/scenario_planning/lane_driving/behavior_planning/behavior_path_planner/behavior_path_planner.param.yaml

@@ -45,6 +45,3 @@
       drivable_area_right_bound_offset: 0.0
       drivable_area_left_bound_offset: 0.0
       drivable_area_types_to_skip: [road_border]
-
-    lane_change:
-      lane_change_prepare_duration: 4.0 # [s]