xfs: remove unused transaction callback variables

We don't do callbacks at transaction commit time, no do we have any
infrastructure to set up or run such callbacks, so remove the
variables and typedefs for these operations. If we ever need to add
callbacks, we can reintroduce the variables at that time.

Signed-off-by: Dave Chinner <[e-mail]>
Reviewed-by: Ben Myers <[e-mail]>
Signed-off-by: Ben Myers <[e-mail]>

fs/xfs/xfs_trans.h

···
 #define XFS_ITEM_FLUSHING	3
 
 /*
- * This is the type of function which can be given to xfs_trans_callback()
- * to be called upon the transaction's commit to disk.
- */
-typedef void (*xfs_trans_callback_t)(struct xfs_trans *, void *);
-
-/*
  * This is the structure maintained for every active transaction.
  */
 typedef struct xfs_trans {
 	unsigned int		t_magic;	/* magic number */
-	xfs_log_callback_t	t_logcb;	/* log callback struct */
 	unsigned int		t_type;		/* transaction type */
 	unsigned int		t_log_res;	/* amt of log space resvd */
 	unsigned int		t_log_count;	/* count for perm log res */