[dart:io] Remove DART_IO_DISABLED

runtime/bin/io_service.cc

 // 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.
 
-#if !defined(DART_IO_DISABLED) && !defined(DART_IO_SECURE_SOCKET_DISABLED)
+#if !defined(DART_IO_SECURE_SOCKET_DISABLED)
 
 #include "bin/io_service.h"
 
 #include "bin/dartutils.h"
 #include "bin/directory.h"
 #include "bin/file.h"
 #include "bin/io_buffer.h"
 #include "bin/secure_socket_filter.h"
 #include "bin/security_context.h"
 #include "bin/socket.h"
@@ skipping 48 matching lines @@
   if (service_port != ILLEGAL_PORT) {
     // Return a send port for the service port.
     Dart_Handle send_port = Dart_NewSendPort(service_port);
     Dart_SetReturnValue(args, send_port);
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // !defined(DART_IO_DISABLED) &&
-        // !defined(DART_IO_SECURE_SOCKET_DISABLED)
+#endif  // !defined(DART_IO_SECURE_SOCKET_DISABLED)