fix: remove existing process hardening from Codex CLI (#8951)

As explained in https://github.com/openai/codex/issues/8945 and
https://github.com/openai/codex/issues/8472, there are legitimate cases
where users expect processes spawned by Codex to inherit environment
variables such as `LD_LIBRARY_PATH` and `DYLD_LIBRARY_PATH`, where
failing to do so can cause significant performance issues.

This PR removes the use of
`codex_process_hardening::pre_main_hardening()` in Codex CLI (which was
added not in response to a known security issue, but because it seemed
like a prudent thing to do from a security perspective:
https://github.com/openai/codex/pull/4521), but we will continue to use
it in `codex-responses-api-proxy`. At some point, we probably want to
introduce a slightly different version of
`codex_process_hardening::pre_main_hardening()` in Codex CLI that
excludes said environment variables from the Codex process itself, but
continues to propagate them to subprocesses.

codex-rs/Cargo.lock

@@ -1156,7 +1156,6 @@ dependencies = [
  "codex-execpolicy",
  "codex-login",
  "codex-mcp-server",
- "codex-process-hardening",
  "codex-protocol",
  "codex-responses-api-proxy",
  "codex-rmcp-client",
@@ -1166,7 +1165,6 @@ dependencies = [
  "codex-utils-absolute-path",
  "codex-utils-cargo-bin",
  "codex-windows-sandbox",
- "ctor 0.5.0",
  "libc",
  "owo-colors",
  "predicates",