How to remove WPMU ad from client dashboard?

WPMU has put a red-lettered notice on the dashboard of one of my client sites. I do not want it there, and neither does he. What do I need to do to remove the notice? The only WPMU plugin we are using on the site is Login image and we don't need the update notifications plugin.

This marketing technique is highly intrusive and unappreciated, by the way.