I'm also looking for a way to remove this message. It wouldn't be so bad if it looked like a regular menu item, but it's styled to stand out (white text on grey background).
Promoting Premium to Free users would be fine, but using a distracting menu item to promote Enterprise to Premium users? That's just annoying. I'm already aware of Enterprise (via newsletters and blog posts), but don't have a need for it. I just want to continue paying $12/year for the wonderful cross-platform, promotion-free LastPass user experience I've grown to love.