[xslocobot_sim] fix double namespace issue

[stephenadhi]

Double namespace issue when launching the simulator:

A quick fix: removing the robot namespace 'locobot/' from the _frameids of the config file, because _gazebo_ros2control already appends the namespace to the frames automatically.

Applied to both create3 and kobuki versions.

[lukeschmitt-tr]

Thanks for the contribution!