Really remove io support when dart:io is unsupported.

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 108fe4cf4a042a2ef63dea08b97eb241959edc43..491fa29114f85672b6415767c868a7c67d03ad03 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_SECURE_SOCKET_DISABLED)
+#if !defined(DART_IO_DISABLED) && !defined(DART_IO_SECURE_SOCKET_DISABLED)
 
 #include "bin/io_service.h"
 
@@ -76,4 +76,5 @@ void FUNCTION_NAME(IOService_NewServicePort)(Dart_NativeArguments args) {
 }  // namespace bin
 }  // namespace dart
 
-#endif  // !defined(DART_IO_SECURE_SOCKET_DISABLED)
+#endif  // !defined(DART_IO_DISABLED) &&
+        // !defined(DART_IO_SECURE_SOCKET_DISABLED)