Smart Lock: Use DeviceSyncClient when displaying 'pairing change' notification

This codepath was using the deprecated CryptAuthDeviceManager, which causes
crashes on M71+.

R=jhawkins@chromium.org

Bug: 908579
Change-Id: I52bd659b43cb851caa696fb77bcf0536396ba214
Reviewed-on: https://chromium-review.googlesource.com/c/1351877Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611392}

chrome/browser/chromeos/login/easy_unlock/easy_unlock_service_regular.cc

@@ -743,13 +743,10 @@ void EasyUnlockServiceRegular::OnScreenDidUnlock(
 
   if (shown_pairing_changed_notification_) {
     shown_pairing_changed_notification_ = false;
-    std::vector<cryptauth::ExternalDeviceInfo> unlock_keys =
-        GetCryptAuthDeviceManager()->GetUnlockKeys();
-    if (!unlock_keys.empty()) {
-      // TODO(tengs): Right now, we assume that there is only one possible
-      // unlock key. We need to update this notification be more generic.
+
+    if (!GetUnlockKeys().empty()) {
       notification_controller_->ShowPairingChangeAppliedNotification(
-          unlock_keys[0].friendly_device_name());
+          GetUnlockKeys()[0].name());
     }
   }