Thanks for bringing this feature to my attention. Must be a recent thing, this promotional product plugging of “Ubuntu Pro”. At least, I didn’t see it before. To be honest, when all goes as it should be, I don’t pay much attention to what apt update or apt upgrade print on the screen.
However it is rather an inappropriate message, and a dangerous bend.
It may be harmless in the thoughts of many, I don’t appreciate it at all. I don’t think the Lubuntu team is to blame for this (but I am not sure).
I could write a long story, a very long essay even, about what I think of it. But I leave it as is, for now. I think It is good thing to have the simple solution to get rid of this annoying message!