test: remove string error from strictEqual

Removes the string error from the assertion call to improve the error
message shown on screen when the test fails.

PR-URL: #21292
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-stream-writableState-uncorked-bufferedRequestCount.js

@@ -7,7 +7,7 @@ const stream = require('stream');
 const writable = new stream.Writable();
 
 writable._writev = common.mustCall((chunks, cb) => {
-  assert.strictEqual(chunks.length, 2, 'two chunks to write');
+  assert.strictEqual(chunks.length, 2);
   cb();
 }, 1);