The client does not plan to add content, so I want to remove or hide this button. Is that possible?
Not possible. Page manager is part of Sitecake.
Maybe you can write some clever CSS to hide it, but it’s up to you.
My mistake. @predragleka just told me that there is a way to remove page manager button.
If you want to disable page manager all together you can do that in editor.cnf file by adding Pagemanager.init = false.