mm: remove stale example from comment

folio_add_new_anon_rmap() no longer works this way, so just remove the
entire example.

Link: https://lkml.kernel.org/r/20231211162214.2146080-6-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memremap.c

@@ -473,21 +473,11 @@ void free_zone_device_page(struct page *page)
 		__ClearPageAnonExclusive(page);
 
 	/*
-	 * When a device managed page is freed, the page->mapping field
+	 * When a device managed page is freed, the folio->mapping field
 	 * may still contain a (stale) mapping value. For example, the
-	 * lower bits of page->mapping may still identify the page as an
-	 * anonymous page. Ultimately, this entire field is just stale
-	 * and wrong, and it will cause errors if not cleared.  One
-	 * example is:
-	 *
-	 *  migrate_vma_pages()
-	 *    migrate_vma_insert_page()
-	 *      page_add_new_anon_rmap()
-	 *        __page_set_anon_rmap()
-	 *          ...checks page->mapping, via PageAnon(page) call,
-	 *            and incorrectly concludes that the page is an
-	 *            anonymous page. Therefore, it incorrectly,
-	 *            silently fails to set up the new anon rmap.
+	 * lower bits of folio->mapping may still identify the folio as an
+	 * anonymous folio. Ultimately, this entire field is just stale
+	 * and wrong, and it will cause errors if not cleared.
 	 *
 	 * For other types of ZONE_DEVICE pages, migration is either
 	 * handled differently or not done at all, so there is no need