[dart:io] Remove DART_IO_DISABLED

runtime/bin/process_win.cc

 // Copyright (c) 2012, 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/process.h"
 
 #include <process.h>  // NOLINT
 #include <psapi.h>    // NOLINT
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
@@ skipping 1021 matching lines @@
   }
   if (signal_handlers == NULL) {
     USE(SetConsoleCtrlHandler(SignalHandler, false));
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_WINDOWS)
-
-#endif  // !defined(DART_IO_DISABLED)