Here's what I see in my Settings:
So it looks like I am stuck with Mastery Paths being on. But I don't want them to be on, or more precisely, I don't want the option to "Allow in mastery paths" to show up when I edit a page:
because if that button to "Allow in mastery paths" gets checked somehow, then the page shows up in the Assignments index (see Why is there a page in my Assignment Index?).
On a related note, is there any way to tell if a something has been "allowed in mastery paths" without editing it (aside from noticing that it is appearing in strange places)?