Fix errors in dart:io tests found by the analyzer

tests/standalone/io/socket_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:async";
@@ skipping 35 matching lines @@
         asyncEnd();
       });
 
   // Bind to a port already in use.
   asyncStart();
   ServerSocket.bind("127.0.0.1", 0)
       .then((s) {
         ServerSocket.bind("127.0.0.1", s.port)
             .then((t) {
               Expect.fail("Multiple listens on same port");
-              port.toSendPort().send(1);
             })
             .catchError((error) {
               Expect.isTrue(error is SocketException);
               s.close();
               asyncEnd();
             });
       });
 }
 
 void testConnectNoDestroy() {
@@ skipping 153 matching lines @@
   testConnectImmediateDestroy();
   testConnectConsumerClose();
   testConnectConsumerWriteClose();
   testConnectStreamClose();
   testConnectStreamDataClose(true);
   testConnectStreamDataClose(false);
   testConnectStreamDataCloseCancel(true);
   testConnectStreamDataCloseCancel(false);
   asyncEnd();
 }