Remove unnecessary friend class declaration

Change-Id: I899bd9c76d5c78835cf14ecbf8bb9670e4cc7bd6
Reviewed-on: https://chromium-review.googlesource.com/c/1341479Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Xi Cheng <chengx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609445}

chrome/browser/notifications/notification_platform_bridge_win.cc

@@ -654,7 +654,6 @@ class NotificationPlatformBridgeWinImpl
 
  private:
   friend class base::RefCountedThreadSafe<NotificationPlatformBridgeWinImpl>;
-  friend class MockIToastNotifier;
   friend class NotificationPlatformBridgeWin;
 
   ~NotificationPlatformBridgeWinImpl() {