xfs: kill XFS_BTREE_MAXLEVELS

Nobody uses this symbol anymore, so kill it.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/libxfs/xfs_btree.h

@@ -92,8 +92,6 @@ uint32_t xfs_btree_magic(int crc, xfs_btnum_t btnum);
 #define XFS_BTREE_STATS_ADD(cur, stat, val)	\
 	XFS_STATS_ADD_OFF((cur)->bc_mp, (cur)->bc_statoff + __XBTS_ ## stat, val)
 
-#define	XFS_BTREE_MAXLEVELS	9	/* max of all btrees */
-
 /*
  * The btree cursor zone hands out cursors that can handle up to this many
  * levels.  This is the known maximum for all btree types.