Drop local-only json_utils from claude.opam + root.opam depends

ocaml-claude/examples/ has '(library (name json_utils))' without a
public_name — a workspace-private library. The opam regen pre-existing
the local-private filter pulled it into ocaml-claude/dune-project's
(depends ...) and the workspace-root dune-project. From there 'json_utils'
shipped in ocaml-claude/claude.opam (and indirectly in root.opam) as if
it were a real opam package, breaking opam install of the package.

Drop it from both dune-project files and let dune regenerate the .opam
files clean. The lint no longer re-introduces it because of 061e856ee.