removed extra extern file_fdatawait_range

Jeff added this extern twice in commit a823e458

Fixes: a823e458 ("mm: add file_fdatawait_range and file_write_and_wait")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fs.h

@@ -2623,8 +2623,6 @@ static inline int filemap_fdatawait(struct address_space *mapping)
 
 extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
 				  loff_t lend);
-extern int __must_check file_fdatawait_range(struct file *file, loff_t lstart,
-						loff_t lend);
 extern int filemap_write_and_wait(struct address_space *mapping);
 extern int filemap_write_and_wait_range(struct address_space *mapping,
 				        loff_t lstart, loff_t lend);