Revert of Update first download notification correctly if there are multiple notifications

chrome/browser/download/notification/download_notification_manager.h

Index: chrome/browser/download/notification/download_notification_manager.h
diff --git a/chrome/browser/download/notification/download_notification_manager.h b/chrome/browser/download/notification/download_notification_manager.h
index 7490c1a0396dd0923b7e81dc37341eb737e2bff4..dbc84e86dfe2c016b4275fad842373331c25859b 100644
--- a/chrome/browser/download/notification/download_notification_manager.h
+++ b/chrome/browser/download/notification/download_notification_manager.h
@@ -45,10 +45,6 @@
       Profile* profile, DownloadNotificationManager* parent_manager);
   ~DownloadNotificationManagerForProfile() override;
 
-  message_center::MessageCenter* message_center() const {
-    return message_center_;
-  }
-
   // DownloadItem::Observer overrides:
   void OnDownloadUpdated(content::DownloadItem* download) override;
   void OnDownloadOpened(content::DownloadItem* download) override;
@@ -60,16 +56,10 @@
  private:
   friend class test::DownloadItemNotificationTest;
 
-  void OverrideMessageCenterForTest(
-      message_center::MessageCenter* message_center);
-
   Profile* profile_ = nullptr;
   DownloadNotificationManager* parent_manager_;  // weak
   std::set<content::DownloadItem*> downloading_items_;
   std::map<content::DownloadItem*, DownloadItemNotification*> items_;
-
-  // Pointer to the message center instance.
-  message_center::MessageCenter* message_center_;
 
   STLValueDeleter<std::map<content::DownloadItem*, DownloadItemNotification*>>
       items_deleter_;