refactor(codex): drop unused prompt overlay wrapper

extensions/codex/prompt-overlay.ts

@@ -4,7 +4,6 @@
 import {
   GPT5_BEHAVIOR_CONTRACT,
   GPT5_HEARTBEAT_PROMPT_OVERLAY,
-  renderGpt5PromptOverlay,
   resolveGpt5SystemPromptContribution,
 } from "openclaw/plugin-sdk/provider-model-shared";
 
@@ -19,10 +18,3 @@ export function resolveCodexSystemPromptContribution(
 ) {
   return resolveGpt5SystemPromptContribution(params);
 }
-
-/** Renders the Codex prompt overlay text for supported GPT-5-family models. */
-export function renderCodexPromptOverlay(
-  params: Parameters<typeof renderGpt5PromptOverlay>[0],
-): string | undefined {
-  return renderGpt5PromptOverlay(params);
-}