[dart:io] Remove DART_IO_DISABLED

runtime/bin/file_system_watcher_fuchsia.cc

Index: runtime/bin/file_system_watcher_fuchsia.cc
diff --git a/runtime/bin/file_system_watcher_fuchsia.cc b/runtime/bin/file_system_watcher_fuchsia.cc
index 67ddfc854102cfcf2d429ec649bd7dea4f034cd2..e38a01e0b7ba4e93dc9123e5202e68d5b95e755c 100644
--- a/runtime/bin/file_system_watcher_fuchsia.cc
+++ b/runtime/bin/file_system_watcher_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)
 
@@ -50,5 +48,3 @@ intptr_t FileSystemWatcher::WatchPath(intptr_t id,
 }  // namespace dart
 
 #endif  // defined(HOST_OS_FUCHSIA)
-
-#endif  // !defined(DART_IO_DISABLED)