Remove InsecureContentInfobarDelegate, which has been broken for a while

chrome/browser/infobars/infobar_service.h

Index: chrome/browser/infobars/infobar_service.h
diff --git a/chrome/browser/infobars/infobar_service.h b/chrome/browser/infobars/infobar_service.h
index a18e157e74adf1d3599577fc4eaa6bbc248bb43e..f6913c59c166e7e56e41160a539187e3d06a4767 100644
--- a/chrome/browser/infobars/infobar_service.h
+++ b/chrome/browser/infobars/infobar_service.h
@@ -75,10 +75,6 @@ class InfoBarService : public infobars::InfoBarManager,
   void NavigationEntryCommitted(
       const content::LoadCommittedDetails& load_details) override;
   void WebContentsDestroyed() override;
-  bool OnMessageReceived(const IPC::Message& message) override;
-
-  // Message handlers.
-  void OnDidBlockDisplayingInsecureContent();
 
   // See description in set_ignore_next_reload().
   bool ignore_next_reload_;