Change page column heading from "Location" to "Page"

I think the term "Location" was an attempt to be general in case the values were
not actually pages. However the VitalSource API field from which we get these
values, the VS EPUB publishers guide [1] and the VS UI all use the term "page",
and the intent is that the values correspond to page numbers in a physical
version of the book.

[1] https://www.vitalsource.com/products/vitalsource-epub3-implementation-guide-vitalsource-vvstdocsepub3implementguide

lms/static/scripts/frontend_apps/components/ChapterList.tsx

@@ -50,7 +50,7 @@ export default function ChapterList({
         field: 'title',
       },
       {
-        label: 'Location',
+        label: 'Page',
         field: 'page',
         classes: 'w-32',
       },