[ios] Removed usused handleDocumentRetitledMessage:context: handler.

BUG=None

Review-Url: https://codereview.chromium.org/2339323002
Cr-Commit-Position: refs/heads/master@{#419241}

ios/web/web_state/ui/crw_web_controller.mm

@@ -2551,8 +2551,6 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
         @selector(handleGeolocationDialogSuppressedMessage:context:);
     (*handlers)["document.favicons"] =
         @selector(handleDocumentFaviconsMessage:context:);
-    (*handlers)["document.retitled"] =
-        @selector(handleDocumentRetitledMessage:context:);
     (*handlers)["document.submit"] =
         @selector(handleDocumentSubmitMessage:context:);
     (*handlers)["externalRequest"] =