NFS: remove nfs_page_lengthg and usage of page_index

This function is no longer used after commit 4fa7a717 ("NFS: Fix up
nfs_vm_page_mkwrite() for folios"), all users have been converted to use
folio instead, just delete it to remove usage of page_index.

Link: https://lkml.kernel.org/r/20240521175854.96038-5-ryncsn@gmail.comSigned-off-by: Kairui Song <kasong@tencent.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Marc Dionne <marc.dionne@auristor.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Xiubo Li <xiubli@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nfs/internal.h

@@ -797,25 +797,6 @@ static inline void nfs_folio_mark_unstable(struct folio *folio,
 	}
 }
 
-/*
- * Determine the number of bytes of data the page contains
- */
-static inline
-unsigned int nfs_page_length(struct page *page)
-{
-	loff_t i_size = i_size_read(page_file_mapping(page)->host);
-
-	if (i_size > 0) {
-		pgoff_t index = page_index(page);
-		pgoff_t end_index = (i_size - 1) >> PAGE_SHIFT;
-		if (index < end_index)
-			return PAGE_SIZE;
-		if (index == end_index)
-			return ((i_size - 1) & ~PAGE_MASK) + 1;
-	}
-	return 0;
-}
-
 /*
  * Determine the number of bytes of data the page contains
  */