chore: remove stray licensing artifact resurrected by #899

#881 deleted libs/licensing in the MIT cutover. #899's commit was staged
with 'git add -A' in a worktree that still carried the untracked
generated public-key file, silently re-adding it. Nothing on main
references the lib (verified: only historical planning docs mention it).

Restores mit-cutover.spec.mjs's 'libs/licensing does not exist'
assertion to truth.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: blove