[dart:io] Remove DART_IO_DISABLED

runtime/bin/file_system_watcher_win.cc

Index: runtime/bin/file_system_watcher_win.cc
diff --git a/runtime/bin/file_system_watcher_win.cc b/runtime/bin/file_system_watcher_win.cc
index dad55c60e7afb76ba118d181b682b5d3ab99fd18..88031f5a527b8b3640710330845717454fbb4f13 100644
--- a/runtime/bin/file_system_watcher_win.cc
+++ b/runtime/bin/file_system_watcher_win.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_WINDOWS)
 
@@ -131,5 +129,3 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
 }  // namespace dart
 
 #endif  // defined(HOST_OS_WINDOWS)
-
-#endif  // !defined(DART_IO_DISABLED)