Remove last traces of ->sync_page

Commit 7eaceaccab5f removed ->sync_page, but a few mentions of it still
existed in documentation and comments,

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index f40972d..e01287c 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1854,7 +1854,7 @@
 	/* Need this to sanity check attribute list references to $MFT. */
 	vi->i_generation = ni->seq_no = le16_to_cpu(m->sequence_number);
 
-	/* Provides readpage() and sync_page() for map_mft_record(). */
+	/* Provides readpage() for map_mft_record(). */
 	vi->i_mapping->a_ops = &ntfs_mst_aops;
 
 	ctx = ntfs_attr_get_search_ctx(ni, m);