mm/hugetlb: remove hugetlb_page_subpool()

All users of hugetlb_page_subpool() have been converted to use the folio
equivalent.  This function can be safely removed.

Link: https://lkml.kernel.org/r/20230516225205.1429196-1-sidhartha.kumar@oracle.comSigned-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/hugetlb.h

@@ -757,14 +757,6 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
 	return folio->_hugetlb_subpool;
 }
 
-/*
- * hugetlb page subpool pointer located in hpage[2].hugetlb_subpool
- */
-static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
-{
-	return hugetlb_folio_subpool(page_folio(hpage));
-}
-
 static inline void hugetlb_set_folio_subpool(struct folio *folio,
 					struct hugepage_subpool *subpool)
 {
@@ -1031,11 +1023,6 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
 	return NULL;
 }
 
-static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
-{
-	return NULL;
-}
-
 static inline int isolate_or_dissolve_huge_page(struct page *page,
 						struct list_head *list)
 {