[dart:io] Remove DART_IO_DISABLED

runtime/bin/io_service.h

 // 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.
 
 #ifndef RUNTIME_BIN_IO_SERVICE_H_
 #define RUNTIME_BIN_IO_SERVICE_H_
 
-#if defined(DART_IO_DISABLED) || defined(DART_IO_SECURE_SOCKET_DISABLED)
+#if defined(DART_IO_SECURE_SOCKET_DISABLED)
 #error "io_service.h can only be included on builds with IO and SSL enabled"
 #endif
 
 #include "bin/builtin.h"
 #include "bin/utils.h"
 
 namespace dart {
 namespace bin {
 
 // This list must be kept in sync with the list in sdk/lib/io/io_service.dart
@@ skipping 52 matching lines @@
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(IOService);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // RUNTIME_BIN_IO_SERVICE_H_