Fix bustage from bug 542337, this function doesn't exist.

widget/src/windows/nsWindow.cpp

@@ -7129,7 +7129,6 @@ void nsWindow::UpdateWindowInternal(HWND aWnd)
       if (instance) {
         if (!instance->CallUpdateWindow())
           NS_ERROR("Failed to send message!");
-        ValidateWindow(aWnd, NULL);
         return;
       }
     }