test: remove unused canvas temp helper

extensions/canvas/scripts/copy-a2ui.test.ts

@@ -1,5 +1,4 @@
 import fs from "node:fs/promises";
-import os from "node:os";
 import path from "node:path";
 import { resolvePreferredOpenClawTmpDir, withTempWorkspace } from "openclaw/plugin-sdk/temp-path";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";