fix: remove ID-based lane link fallback

RLS previously guessed a lane's predecessor/successor by checking whether a lane with the same numeric ID existed in the adjacent lane section when the .xodr omitted an explicit element.

This goes against the standard (ASAM OpenDRIVE 11.6) and caused GtGenMap to fabricate a predecessor/successor for lanes that legitimately begin or end within a lane section whenever an unrelated lane got renumbered to the same ID.

Consider only explicit elements now.