[Remote user wipe] Update wrong year on one file (2014 -> 2018)

This was a mistake on my part when writing the original file, and it
was just too bothering to see the wrong year on the file and get
confused by it, so I had to update it :-)

Change-Id: Ia59fd264f11bda490448a386528b9b2fc0606473
Reviewed-on: https://chromium-review.googlesource.com/c/1326641Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Ivan Šandrk <isandrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606587}

chrome/browser/chromeos/system/user_removal_manager.cc

-// Copyright 2014 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.