test: improve assert message

Use the default assert.strictEqual() message so that unequal values are
shown in the event of an AssertionError.

PR-URL: nodejs#19629
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-http-client-timeout-agent.js

@@ -89,6 +89,6 @@ server.listen(0, options.host, function() {
 
 process.on('exit', function() {
   console.error(`done=${requests_done} sent=${requests_sent}`);
-  assert.strictEqual(requests_done, requests_sent,
-                     'timeout on http request called too much');
+  // check that timeout on http request was not called too much
+  assert.strictEqual(requests_done, requests_sent);
 });