[dart:io] Remove DART_IO_DISABLED

runtime/bin/eventhandler_unsupported.cc

-// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
-// 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 "bin/eventhandler.h"
-
-#include "bin/builtin.h"
-#include "bin/dartutils.h"
-#include "include/dart_api.h"
-
-namespace dart {
-namespace bin {
-
-void EventHandler::Start() {}
-
-void EventHandler::Stop() {}
-
-void FUNCTION_NAME(EventHandler_SendData)(Dart_NativeArguments args) {
-  Dart_ThrowException(DartUtils::NewInternalError(
-      "EventHandler is not supported on this platform"));
-}
-
-void FUNCTION_NAME(EventHandler_TimerMillisecondClock)(
-    Dart_NativeArguments args) {
-  Dart_ThrowException(DartUtils::NewInternalError(
-      "EventHandler is not supported on this platform"));
-}
-
-}  // namespace bin
-}  // namespace dart
-
-#endif  // defined(DART_IO_DISABLED)