[dart:io] Remove DART_IO_DISABLED

runtime/bin/process_fuchsia.cc

Index: runtime/bin/process_fuchsia.cc
diff --git a/runtime/bin/process_fuchsia.cc b/runtime/bin/process_fuchsia.cc
index f994d01f604282ab04c6b2385e4e931b7c9560b9..0f618b513a2d4c90c300b95ffc07cc77f3cea365 100644
--- a/runtime/bin/process_fuchsia.cc
+++ b/runtime/bin/process_fuchsia.cc
@@ -2,8 +2,6 @@
 // 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_FUCHSIA)
 
@@ -740,5 +738,3 @@ void Process::ClearSignalHandler(intptr_t signal, Dart_Port port) {}
 }  // namespace dart
 
 #endif  // defined(HOST_OS_FUCHSIA)
-
-#endif  // !defined(DART_IO_DISABLED)