At the moment, it is not an option to remove or add the list of enrolled to the custom menu. But since it is a customization of the custom menu render, you can remove it easily.
Go to Archaius folder, then, open the file called renderers.php. You just have to comment of remove the following part of the code:
You only have to remove the code from line 103-120.
Important
If you don´t have experience as a developer, save a copy of the original file and make a test first in your testing server.
Something better
It could be nicer if you have the option to show this option only for students and present the list by categories. If you have the same opinion of a better solution, report it as a improvement in:
https://github.com/dmuneras/moodle-theme_archaius/issues
Hope it helps.
