[dart:io] Remove DART_IO_DISABLED

runtime/bin/file_system_watcher_android.cc

Index: runtime/bin/file_system_watcher_android.cc
diff --git a/runtime/bin/file_system_watcher_android.cc b/runtime/bin/file_system_watcher_android.cc
index 561c0d42e86192a39a8ae79c88987c7286113570..08619f2b21efd8f9b7d4ecbe725691742fe7c8c2 100644
--- a/runtime/bin/file_system_watcher_android.cc
+++ b/runtime/bin/file_system_watcher_android.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_ANDROID)
 
@@ -141,5 +139,3 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
 }  // namespace dart
 
 #endif  // defined(HOST_OS_ANDROID)
-
-#endif  // !defined(DART_IO_DISABLED)