[CrOS MultiDevice]: Remove unnecessary BUILD files

Two new BUILD files, namely
chrome/browser/chromeos/device_sync/BUILD.gn and
chrome/browser/chromeos/multidevice_setup/BUILD.gn

Are already in the parent directory's BUILD and we mistakenly added
separately as well:

https://cs.chromium.org/chromium/src/chrome/browser/chromeos/BUILD.gn?l=584
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/BUILD.gn?l=1277

Change-Id: Ia9499d229eb4d6e09f406d784a791b732efaee34
Reviewed-on: https://chromium-review.googlesource.com/1147431
Commit-Queue: Jordy Greenblatt <jordynass@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577303}

chrome/browser/chromeos/device_sync/BUILD.gn

-# 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.
-
-static_library("device_sync") {
-  sources = [
-    "device_sync_client_factory.cc",
-    "device_sync_client_factory.h",
-  ]
-
-  deps = [
-    "//chromeos/services/device_sync/public/cpp/",
-  ]
-}

chrome/browser/chromeos/multidevice_setup/BUILD.gn

-# 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.
-
-component("multidevice_setup") {
-  sources = [
-    "multidevice_setup_client_factory.cc",
-    "multidevice_setup_client_factory.h",
-  ]
-
-  deps = [
-    "//chromeos/services/multidevice_setup/public/cpp",
-  ]
-}