[dart:io] Remove DART_IO_DISABLED

runtime/bin/process_macos.cc

Index: runtime/bin/process_macos.cc
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index b59a0f094d07d6d1ce66ea661cdd29da1d6748bc..c888730d03bac892eec7d495770ac86a35fe1ece 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.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_MACOS)
 
@@ -1082,5 +1080,3 @@ void Process::ClearSignalHandler(intptr_t signal, Dart_Port port) {
 }  // namespace dart
 
 #endif  // defined(HOST_OS_MACOS)
-
-#endif  // !defined(DART_IO_DISABLED)