Bug 577823 - [Robotics, ROS2] non-referenced functions in the model create code artifacts

- Remove unreferenced functions from temporary model prior to generation
- Might ask the user in the future via a different patch set (keep bug open)

Change-Id: I3481f4110933008f3fb63986c9fbff102967bb01
Signed-off-by: Ansgar Radermacher <ansgar.radermacher@cea.fr>