Mash cleanup: message center part 2.

Move ShowLockScreenNotificationSettings, which has little to do with the
rest of the AshMessageCenterController/Client, to LoginScreenClient.

TBR=tsepez@chromium.org

Bug: 958191
Change-Id: I211a1c89d8dc15b2315132152ea32d27770aeb7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1650955
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668165}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index 9b795ec8..d7d0fbb 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -398,6 +398,10 @@
   client_->ShowAccountAccessHelpApp();
 }
 
+void LoginScreenController::ShowLockScreenNotificationSettings() {
+  client_->ShowLockScreenNotificationSettings();
+}
+
 void LoginScreenController::FocusOobeDialog() {
   if (!client_)
     return;