Follow-up to #38089. The merged PR removed --recurse-submodules from the
installer, CI, and getting-started docs, but missed the same stale clause in:
- CONTRIBUTING.md (Prerequisites table)
- website/docs/developer-guide/contributing.md (table + clone command)
- zh-Hans mirror of the developer-guide contributing doc
git-lfs is kept in the Git requirement rows since it's a separate, real
prerequisite. No .gitmodules has existed since the Atropos RL submodule was
removed in #26106.
