[codex] Revert shared BuildBuddy Bazel wrapper (#25909)

## Why

PR #25905 intentionally adds a failing `codex-core` unit test, but its
[Bazel test on Windows
check](https://github.com/openai/codex/actions/runs/26837526950/job/79135369259)
passed. That shows the Bazel configuration introduced by #25156 is not
behaving as expected, so revert it while the configuration can be
investigated separately.

## What changed

Revert #25156 in full, restoring the previous Bazel remote
configuration, CI scripts, workflows, `rusty_v8` handling, and
documentation. This removes the shared BuildBuddy wrapper and its tests.

## Validation

Not run locally; this exact revert was prioritized for a fast rollback.

.github/workflows/bazel.yml

@@ -15,7 +15,6 @@ concurrency:
   # See https://docs.github.com/en/actions/using-jobs/using-concurrency and https://docs.github.com/en/actions/learn-github-actions/contexts for more info.
   group: concurrency-group::${{ github.workflow }}::${{ github.event.pull_request.number > 0 && format('pr-{0}', github.event.pull_request.number) || github.ref_name }}${{ github.ref_name == 'main' && format('::{0}', github.run_id) || ''}}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
-
 jobs:
   test:
     # PRs use the sharded Windows cross-compiled test jobs below. Post-merge
@@ -56,17 +55,12 @@ jobs:
           ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.sha }}
           persist-credentials: false
 
-      - uses: taiki-e/install-action@44c6d64aa62cd779e873306675c7a58e86d6d532 # v2.62.49
-        if: matrix.os == 'ubuntu-24.04' && matrix.target == 'x86_64-unknown-linux-gnu'
-        with:
-          tool: just
-
       - name: Check rusty_v8 MODULE.bazel checksums
         if: matrix.os == 'ubuntu-24.04' && matrix.target == 'x86_64-unknown-linux-gnu'
         shell: bash
         run: |
           python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
-          just test-github-scripts
+          python3 -m unittest discover -s .github/scripts -p test_rusty_v8_bazel.py
 
       - name: Prepare Bazel CI
         id: prepare_bazel