Remove use of using in examples and use hardware_interface::CallbackReturn instead

[destogl]

With changes in ros-controls/ros2_control/pull/673 we had to add additional using in examples for the code to be compilable.

@fmauch gave us a great idea here, to actually use hardware_interface::CallbackReturn instead. This is much more future-proof!

Here you should do the following:

• remove all using CallbackReturn = rclcpp_lifecycle::node_interfaces::LifecycleNodeInterface::CallbackReturn; definition from examples
• use hardware_interface::CallbackReturn instead of CallbackReturn in the delcarations and definitions and for constants-access.