xfs: xfs_fsops: drop useless LIST_HEAD

Drop LIST_HEAD where the variable it declares is never used.

Commit 0410c3bb2b ("xfs: factor ag btree root block
initialisation") stopped using buffer_list and started using a
buffer list in an aghdr_init_data structure, but the declaration
of buffer_list was not removed.

The semantic patch that fixes this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
identifier x;
@@
- LIST_HEAD(x);
  ... when != x
// </smpl>

Fixes: 0410c3bb2b ("xfs: factor ag btree root block initialisation")
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_fsops.c

@@ -40,7 +40,6 @@ xfs_growfs_data_private(
 	xfs_rfsblock_t		new;
 	xfs_agnumber_t		oagcount;
 	xfs_trans_t		*tp;
-	LIST_HEAD		(buffer_list);
 	struct aghdr_init_data	id = {};
 
 	nb = in->newblocks;