I still think it is easier to just disable room creation in Openfire settings. But do as you wish, though i doubt you will get a suggestion how to remove MUC out of Openfire here. Not many developers here and especially for such questions. I’m not a developer myself.
If you are going to use Smack library for your client, then you can ask in the Smack Dev section about creating a client without MUC (again, no guarantees to get many suggestions soon). If you are going to use some other library, then i think you should ask on that library’s site/forums. Btw, i didn’t find anything about client-client chat at the site you gave the link to. Actually creating a client with such scheme would go against the jabber/xmpp nature being a server centric platform (except for file transfers).