Redundant calls to controller_manager spawner

[mhubii]

The controller_manager spawner executable supports a list of controllers, currently, multiple redundant calls are made:

lbr_fri_ros2_stack/lbr_bringup/launch/hardware.launch.py

Line 34 in 808bb07

# controllers on ros2 control node start

See ros-controls/ros2_control_demos#982 (comment).

Furthermore, one may consider declarative launch files.