xfs: kill the unused XFS_BB_FSB_OFFSET macro

Removing the macro, as this is no more needed in the code.
Tried to find the reference when it was last used - but the usage
for this seemed to have been dropped long time ago.
Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_sb.h

@@ -529,7 +529,6 @@ static inline int xfs_sb_version_hasprojid32bit(xfs_sb_t *sbp)
 #define	XFS_BB_TO_FSB(mp,bb)	\
 	(((bb) + (XFS_FSB_TO_BB(mp,1) - 1)) >> (mp)->m_blkbb_log)
 #define	XFS_BB_TO_FSBT(mp,bb)	((bb) >> (mp)->m_blkbb_log)
-#define	XFS_BB_FSB_OFFSET(mp,bb) ((bb) & ((mp)->m_bsize - 1))
 
 /*
  * File system block to byte conversions.