Fixes#7759:
- Drop the stale `rmcp` entry from `codex-rs/default.nix`’s
`cargoLock.outputHashes` since the crate now comes from crates.io and no
longer needs a git hash.
- Add the missing hash for the filedescriptor-0.8.3 git dependency (from
`pakrym/wezterm`) so `buildRustPackage` can vendor it.