[dart:io] Remove DART_IO_DISABLED

runtime/bin/io_service.cc

Index: runtime/bin/io_service.cc
diff --git a/runtime/bin/io_service.cc b/runtime/bin/io_service.cc
index d77e81d35e6a6733797cb42814d033cf347c951f..9c13d645c2f7beadb96a4031ff36e0ba28353985 100644
--- a/runtime/bin/io_service.cc
+++ b/runtime/bin/io_service.cc
@@ -2,7 +2,7 @@
 // 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"
 
@@ -71,5 +71,4 @@ void FUNCTION_NAME(IOService_NewServicePort)(Dart_NativeArguments args) {
 }  // namespace bin
 }  // namespace dart
 
-#endif  // !defined(DART_IO_DISABLED) &&
-        // !defined(DART_IO_SECURE_SOCKET_DISABLED)
+#endif  // !defined(DART_IO_SECURE_SOCKET_DISABLED)