[codex] Remove Codex SDK canary runtime (#220)

* Revert "fix: drain sdk follow-up turns (#219)"

This reverts commit 807828e0ce.

* Revert "feat: feature-flag Codex SDK runner (#218)"

This reverts commit 879d16235f.

src/message-agent-executor-attempt-runner.ts

@@ -100,7 +100,6 @@ interface RunMessageAgentAttemptArgs {
       : never,
     processName: string,
     ipcDir?: string,
-    options?: { drainFollowUpsAfterRun?: boolean },
   ) => void;
   onOutput?: (output: AgentOutput) => Promise<void>;
   pairedExecutionLifecycle: {