Fix key duplication in moveit_setup_assistant for moveit_controllers.yaml for typeFollowJointTrajectory

[cschindlbeck]

Description

Moveit Setup Assistant generates duplicated keys action_ns, default for the type FollowJointTrajectory, e.g.

# MoveIt uses this configuration for controller management

moveit_controller_manager: moveit_simple_controller_manager/MoveItSimpleControllerManager

moveit_simple_controller_manager:
  controller_names:
    - steering_controller

  steering_controller:
    type: FollowJointTrajectory
    action_ns: follow_joint_trajectory
    default: true
    joints:
      - front_left_steer_joint
      - front_right_steer_joint
    action_ns: follow_joint_trajectory
    default: true

This PR deletes the redundant keys