feat: remove the GitHub action that runs Codex for now (#2729)

There are some design issues with this action, so until we work them
out, we'll remove this code from the repository to avoid folks from
taking a dependency on it.

.github/workflows/codex.yml

@@ -1,64 +0,0 @@
-name: Codex
-
-on:
-  issues:
-    types: [opened, labeled]
-  pull_request:
-    branches: [main]
-    types: [labeled]
-
-jobs:
-  codex:
-    # This `if` check provides complex filtering logic to avoid running Codex
-    # on every PR. Admittedly, one thing this does not verify is whether the
-    # sender has write access to the repo: that must be done as part of a
-    # runtime step.
-    #
-    # Note the label values should match the ones in the .github/codex/labels
-    # folder.
-    if: |
-      (github.event_name == 'issues' && (
-        (github.event.action == 'labeled' && (github.event.label.name == 'codex-attempt' || github.event.label.name == 'codex-triage'))
-      )) ||
-      (github.event_name == 'pull_request' && github.event.action == 'labeled' && (github.event.label.name == 'codex-review' || github.event.label.name == 'codex-rust-review'))
-    runs-on: ubuntu-latest
-    permissions:
-      contents: write # can push or create branches
-      issues: write # for comments + labels on issues/PRs
-      pull-requests: write # for PR comments/labels
-    steps:
-      # TODO: Consider adding an optional mode (--dry-run?) to actions/codex
-      # that verifies whether Codex should actually be run for this event.
-      # (For example, it may be rejected because the sender does not have
-      # write access to the repo.) The benefit would be two-fold:
-      # 1. As the first step of this job, it gives us a chance to add a reaction
-      #    or comment to the PR/issue ASAP to "ack" the request.
-      # 2. It saves resources by skipping the clone and setup steps below if
-      #    Codex is not going to run.
-
-      - name: Checkout repository
-        uses: actions/checkout@v5
-
-      - uses: dtolnay/rust-toolchain@1.89
-        with:
-          targets: x86_64-unknown-linux-gnu
-          components: clippy
-
-      - uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/registry/index/
-            ~/.cargo/registry/cache/
-            ~/.cargo/git/db/
-            ${{ github.workspace }}/codex-rs/target/
-          key: cargo-ubuntu-24.04-x86_64-unknown-linux-gnu-dev-${{ hashFiles('**/Cargo.lock') }}
-
-      # Note it is possible that the `verify` step internal to Run Codex will
-      # fail, in which case the work to setup the repo was worthless :(
-      - name: Run Codex
-        uses: ./.github/actions/codex
-        with:
-          openai_api_key: ${{ secrets.CODEX_OPENAI_API_KEY }}
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          codex_home: ./.github/codex/home