Remove UserPolicyDiskCache; it is not used.

chrome/browser/chromeos/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//printing/features/features.gni")
 import("//third_party/protobuf/proto_library.gni")
@@ skipping 1130 matching lines @@
     "policy/user_cloud_policy_store_chromeos.cc",
     "policy/user_cloud_policy_store_chromeos.h",
     "policy/user_cloud_policy_token_forwarder.cc",
     "policy/user_cloud_policy_token_forwarder.h",
     "policy/user_cloud_policy_token_forwarder_factory.cc",
     "policy/user_cloud_policy_token_forwarder_factory.h",
     "policy/user_network_configuration_updater.cc",
     "policy/user_network_configuration_updater.h",
     "policy/user_network_configuration_updater_factory.cc",
     "policy/user_network_configuration_updater_factory.h",
-    "policy/user_policy_disk_cache.cc",
-    "policy/user_policy_disk_cache.h",
     "policy/user_policy_manager_factory_chromeos.cc",
     "policy/user_policy_manager_factory_chromeos.h",
     "policy/user_policy_token_loader.cc",
     "policy/user_policy_token_loader.h",
     "policy/wildcard_login_checker.cc",
     "policy/wildcard_login_checker.h",
     "power/cpu_data_collector.cc",
     "power/cpu_data_collector.h",
     "power/extension_event_observer.cc",
     "power/extension_event_observer.h",
@@ skipping 584 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }