[dart:io] Remove DART_IO_DISABLED

runtime/bin/socket_base.cc

 // Copyright (c) 2017, 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)
-
 #include "bin/socket_base.h"
 
 #include "bin/dartutils.h"
 #include "bin/io_buffer.h"
 #include "bin/isolate_data.h"
 #include "bin/lockers.h"
 #include "bin/thread.h"
 #include "bin/utils.h"
 
 #include "include/dart_api.h"
@@ skipping 155 matching lines @@
 
 void FUNCTION_NAME(SocketBase_IsBindError)(Dart_NativeArguments args) {
   intptr_t error_number =
       DartUtils::GetIntptrValue(Dart_GetNativeArgument(args, 1));
   bool is_bind_error = SocketBase::IsBindError(error_number);
   Dart_SetReturnValue(args, is_bind_error ? Dart_True() : Dart_False());
 }
 
 }  // namespace bin
 }  // namespace dart
-
-#endif  // !defined(DART_IO_DISABLED)