That is no longer an option I am afraid. I am trying to streamline and standardize the mIRC interface over the next few versions and part of that involves removing a number of micro-options that generally make the interface less clear/intuitive. In this case, it is often important to know, at a glance, the nickname that you are currently using on the server, especially since your nickname can change for a number of reasons, so the option to hide this information has been removed.
