test: remove unneeded bind() and related comments

As mentioned in the comment of the changed file, "a libuv limitation
makes it necessary to bind()". But, that is not the case in this test.
The subsequent call to send() results in an implicit bind().

PR-URL: https://github.com/nodejs/node/pull/5023


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>