test: fixup flaky test-performance-function-async test

The time assertion was inaccurate. Just remove it as it's
not strictly necessary

PR-URL: #37493
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>

Author: jasnell

test/parallel/test-performance-function-async.js

@@ -26,7 +26,6 @@ async function doIt() {
 const obs = new PerformanceObserver(common.mustCall((list) => {
   const entry = list.getEntries()[0];
   assert.strictEqual(entry.name, 'doIt');
-  assert(entry.duration > 100);
   assert(check);
   obs.disconnect();
 }));