The options is still there. However, it does not show up if there are no .txt files in your mIRC directory.
So either the .txt files are no longer where they used to be, or the location of $mircdir has changed (which is likely, since by default the directory mIRC now uses, for compatibility, is located in 'Application Data').
Type this in mIRC: //echo -a $mircdir (or //run $mircdir). Your .txt files need to be in this directory for everything to work ok.