xfs: remove the unused SYNCHRONIZE macro

There are no callers of the SYNCHRONIZE() macro, so remove it.
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_linux.h

@@ -123,7 +123,6 @@ typedef __u32			xfs_nlink_t;
 #define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
 #define EFSBADCRC	EBADMSG		/* Bad CRC detected */
 
-#define SYNCHRONIZE()	barrier()
 #define __return_address __builtin_return_address(0)
 
 /*