test: fix flaky test by removing timer

This fixes one of the tests that has been failing on CI on freebsd for
a bit by removing an unnecessary timer.

PR-URL: https://github.com/nodejs/node/pull/9199
Fixes: https://github.com/nodejs/node/issues/7929
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-dgram-send-callback-buffer.js

@@ -9,14 +9,9 @@ const client = dgram.createSocket('udp4');
 const buf = Buffer.allocUnsafe(256);
 
 const onMessage = common.mustCall(function(err, bytes) {
-  assert.strictEqual(err, null);
-  assert.equal(bytes, buf.length);
-  clearTimeout(timer);
+  assert.ifError(err);
+  assert.strictEqual(bytes, buf.length);
   client.close();
 });
 
-const timer = setTimeout(function() {
-  throw new Error('Timeout');
-}, common.platformTimeout(200));
-
 client.send(buf, common.PORT, common.localhostIPv4, onMessage);