docs: Drop unused static/templates files.

- static/favicon.ico — exact duplicate of static/openmv.ico (we use
  openmv.ico for html_favicon); remove the duplicate.
- templates/versions.html — old sphinx-rtd-theme language and external-
  links dropdown widget; unreferenced and not rendered by Shibuya.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kwagyeman