Login to your mattermost server via ssh, go to where you installed it and run:
bin/mattermost user delete mattermost-advisor
Answer YES with capitals to whatever it asks for twice. Bye annoying advisor.
Note: They will most likely patch this after they notice it can actually be disabled. Oh well, I guess next time we’ll just have to rebuild the entire mattermost binary because, you know, annoying their customers with useless features gets them new users.
Hint: It doesn’t. In fact it’s a surefire way to get people to migrate to other platforms.