Disable KRecentDocument:add

It's too slow, not ready for production usage

apps/lib/katemainwindow.cpp

@@ -1416,6 +1416,8 @@ void KateMainWindow::addRecentOpenedFile(const QUrl &url)
     // to our local list, aka menu
     m_fileOpenRecent->addUrl(url);
 
+    /** FIXME Disabled because this can be too slow 100ms/doc sometimes,
+     renable when it is 0/ms again*/
     // to the global "Recent Document Menu", see bug 420504
-    KRecentDocument::add(url);
+    // KRecentDocument::add(url);
 }