Revert of ash: Use system tray mojo interface to show system update tray icon

ash/public/interfaces/update.mojom

Index: ash/public/interfaces/update.mojom
diff --git a/ash/public/interfaces/update.mojom b/ash/public/interfaces/update.mojom
deleted file mode 100644
index dd52e5033cadad36ae881dd3f6c896f4336caf5e..0000000000000000000000000000000000000000
--- a/ash/public/interfaces/update.mojom
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-module ash.mojom;
-
-// Urgency of a pending software update. Sets the system tray update icon color.
-// TODO(jamescook): UpgradeDetector::UpgradeNotificationAnnoyanceLevel could be
-// replaced with this if this moves into a component shared with non-ash chrome.
-enum UpdateSeverity {
-  NONE,
-  LOW,
-  ELEVATED,
-  HIGH,
-  SEVERE,
-  CRITICAL,
-};