test: drop stray HTML fixture with no tracked input
The regenerate step picked up an untracked local example-docs JSON and
emitted a fixture (local-single-file/example-docs/.../UDHR_first_article_all.txt.html)
that CI can't reproduce, causing an 'Only in expected-output' diff. Remove
it so every tracked fixture maps to a tracked input.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
