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>

test/internet/test-dgram-multicast-multi-process.js

@@ -132,10 +132,6 @@ if (process.argv[2] !== 'child') {
   }
 
   var sendSocket = dgram.createSocket('udp4');
-  // FIXME: a libuv limitation makes it necessary to bind()
-  // before calling any of the set*() functions. The bind()
-  // call is what creates the actual socket.
-  sendSocket.bind();
 
   // The socket is actually created async now.
   sendSocket.on('listening', function() {