Remove CODEOWNERS

No branch on the repo is protected and there are no rulesets, so the
file never enforced owner review. Its only effect was auto-requesting a
review from the other owner on every PR, which nobody acted on.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.github/CODEOWNERS

@@ -1,2 +0,0 @@
-# Merges to protected branches need sign-off from an org owner.
-* @dhh @ryanrhughes