js_repl: remove codex.state helper references (#12275)

## Summary

This PR removes `codex.state` from the `js_repl` helper surface and
removes all corresponding documentation/instruction references.

## Motivation

Top-level bindings in `js_repl` now persist across cells, so the extra
`codex.state` helper is redundant and adds unnecessary API/docs surface.

## Changes

- Removed the long-lived `state` object from the Node kernel helper
wiring.
- Stopped exposing `codex.state` (and `context.state`) during `js_repl`
execution.
- Updated user-facing `js_repl` docs to remove `codex.state`.
- Updated generated instruction text and related test expectations to
list only:
  - `codex.tmpDir`
  - `codex.tool(name, args?)`


#### [git stack](https://github.com/magus/git-stack-cli)
- ✅ `1` https://github.com/openai/codex/pull/12300
- 👉 `2` https://github.com/openai/codex/pull/12275
- ⏳ `3` https://github.com/openai/codex/pull/12205
- ⏳ `4` https://github.com/openai/codex/pull/12185
- ⏳ `5` https://github.com/openai/codex/pull/10673

docs/js_repl.md

@@ -63,7 +63,6 @@ For `CODEX_JS_REPL_NODE_MODULE_DIRS` and `js_repl_node_module_dirs`, module reso
 
 `js_repl` exposes these globals:
 
-- `codex.state`: mutable object persisted for the current kernel session.
 - `codex.tmpDir`: per-session scratch directory path.
 - `codex.tool(name, args?)`: executes a normal Codex tool call from inside `js_repl` (including shell tools like `shell` / `shell_command` when available).
 - To share generated images with the model, write a file under `codex.tmpDir`, call `await codex.tool("view_image", { path: "/absolute/path" })`, then delete the file.