Fixed copyright message in AOMContentAXTree by removing the (C) symbol

Chromium's new copyright message doesn't have a (C) symbol.
Files created in the last few years should be using the new copyright message.
TBR=dmazzoni@chromium.org, aleventhal@chromium.org

Change-Id: I653ea93d569c8eb21810007dad9df1021d9cf532
Reviewed-on: https://chromium-review.googlesource.com/c/1467024
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631306}
diff --git a/content/renderer/accessibility/aom_content_ax_tree.cc b/content/renderer/accessibility/aom_content_ax_tree.cc
index 1ff0d05..a23339d 100644
--- a/content/renderer/accessibility/aom_content_ax_tree.cc
+++ b/content/renderer/accessibility/aom_content_ax_tree.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2018 The Chromium Authors. All rights reserved.
+// Copyright 2018 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.
 
diff --git a/content/renderer/accessibility/aom_content_ax_tree.h b/content/renderer/accessibility/aom_content_ax_tree.h
index 1c5205c..10865fc 100644
--- a/content/renderer/accessibility/aom_content_ax_tree.h
+++ b/content/renderer/accessibility/aom_content_ax_tree.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2018 The Chromium Authors. All rights reserved.
+// Copyright 2018 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.