Remove legacy dev files: eden.ini, to_do_list, PLAN.md

eden.ini fed the dormant Euclid EDEN packaging (edenise.py, 2023, not in CI);
to_do_list and PLAN.md were stale dev scratch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 2 people