[dart:io] Remove DART_IO_DISABLED

runtime/bin/stdio.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)
-
 #include "bin/stdio.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 #include "bin/utils.h"
 
 #include "include/dart_api.h"
 
 #include "platform/globals.h"
 #include "platform/utils.h"
@@ skipping 93 matching lines @@
   bool supported = false;
   if (Stdout::AnsiSupported(fd, &supported)) {
     Dart_SetBooleanReturnValue(args, supported);
   } else {
     Dart_SetReturnValue(args, DartUtils::NewDartOSError());
   }
 }
 
 }  // namespace bin
 }  // namespace dart
-
-#endif  // !defined(DART_IO_DISABLED)