Simplify profiling and add serverless target (#7007)

I'm using this to profile right now, so it's probably good to update it.

test/integration/profiling/next.config.js

 module.exports = {
+  target: 'serverless',
   experimental: {
     profiling: true
   },

test/integration/profiling/pages/about.js

-export default () => (
-  <div className='about-page'>About Page</div>
-)