[dart:io] Remove DART_IO_DISABLED

runtime/bin/stdio_win.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 "platform/globals.h"
 #if defined(HOST_OS_WINDOWS)
 
 #include "bin/stdio.h"
 
 // These are not always defined in the header files. See:
 // https://msdn.microsoft.com/en-us/library/windows/desktop/ms686033(v=vs.85).aspx
 #ifndef ENABLE_VIRTUAL_TERMINAL_INPUT
 #define ENABLE_VIRTUAL_TERMINAL_INPUT 0x0200
 #endif
@@ skipping 115 matching lines @@
     return true;
   }
   *supported = (mode & ENABLE_VIRTUAL_TERMINAL_PROCESSING) != 0;
   return true;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_WINDOWS)
-
-#endif  // !defined(DART_IO_DISABLED)