test: drop fallback for import.meta.dirname in example code (#2781)

I was following this example in our internal repo and Greptile caught
this error -- we were using dirname without importing it. That fallback
seems to be only for Node 19 and below so it should be safe to drop it

### Changes are visible to end-users: no

### Test plan

- Covered by existing test cases

Co-authored-by: Tyler Breisacher <matrixfrog@gmail.com>

Author: tyler-breisacher-zipline

examples/nextjs/next.standalone.mjs

@@ -1,9 +1,7 @@
 import { join } from 'node:path'
 
-const appDir = import.meta.dirname || dirname(fileURLToPath(import.meta.url))
-
 // Must include the parent .aspect_rules_js package store when tracing for standalone output
-const outputFileTracingRoot = join(appDir, '../../')
+const outputFileTracingRoot = join(import.meta.dirname, '../../')
 
 /** @type {import('next').NextConfig} */
 const nextConfig = {