test: remove unnecessary timer

The timer in NAPI's test_callback_scope/test-resolve-async.js
can be removed. If the test fails, it will timeout on its own.
The extra timer increases the chances of the test being
flaky.

PR-URL: #18719
Fixes: #18702
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/addons-napi/test_callback_scope/test-resolve-async.js

@@ -1,13 +1,6 @@
 'use strict';
 
 const common = require('../../common');
-const assert = require('assert');
 const { testResolveAsync } = require(`./build/${common.buildType}/binding`);
 
-let called = false;
-testResolveAsync().then(common.mustCall(() => {
-  called = true;
-}));
-
-setTimeout(common.mustCall(() => { assert(called); }),
-           common.platformTimeout(20));
+testResolveAsync().then(common.mustCall());