Remove accessible name computation, and use accessible_name value

ag/12295631 refines accessible name computation, therefore we should
not compute accessible_name in two different places.

Bug: b/162193325
Test: None
Change-Id: I466e7c32f47e5578eb38015118a5d598c218a7ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2336000
Commit-Queue: Sara Kato <sarakato@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796589}

ash/public/cpp/external_arc/message_center/arc_notification_item_impl.cc

@@ -92,8 +92,10 @@ void ArcNotificationItemImpl::OnUpdatedFromAndroid(
   if (data->small_icon)
     rich_data.small_image = gfx::Image::CreateFrom1xBitmap(*data->small_icon);
 
-  rich_data.accessible_name = base::UTF8ToUTF16(
-      data->accessible_name.value_or(data->title + "\n" + data->message));
+  if (data->accessible_name.has_value())
+    rich_data.accessible_name =
+        base::UTF8ToUTF16(data->accessible_name.value());
+
   if (manager_->IsOpeningSettingsSupported() && !is_setting_shown) {
     rich_data.settings_button_handler =
         message_center::SettingsButtonHandler::DELEGATE;