btrfs: remove the unused endio_raid56_workers and btrfs_raid_bio::end_io_work

Since we have switched all raid56 workload to submit-and-wait method,
there is no use for btrfs_fs_info::endio_raid56_workers workqueue and
btrfs_raid_bio::end_io_work.

Remove them to save some memory.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -2097,8 +2097,6 @@ static void btrfs_stop_all_workers(struct btrfs_fs_info *fs_info)
 	btrfs_destroy_workqueue(fs_info->workers);
 	if (fs_info->endio_workers)
 		destroy_workqueue(fs_info->endio_workers);
-	if (fs_info->endio_raid56_workers)
-		destroy_workqueue(fs_info->endio_raid56_workers);
 	if (fs_info->rmw_workers)
 		destroy_workqueue(fs_info->rmw_workers);
 	if (fs_info->compressed_write_workers)
@@ -2304,8 +2302,6 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info)
 		alloc_workqueue("btrfs-endio", flags, max_active);
 	fs_info->endio_meta_workers =
 		alloc_workqueue("btrfs-endio-meta", flags, max_active);
-	fs_info->endio_raid56_workers =
-		alloc_workqueue("btrfs-endio-raid56", flags, max_active);
 	fs_info->rmw_workers = alloc_workqueue("btrfs-rmw", flags, max_active);
 	fs_info->endio_write_workers =
 		btrfs_alloc_workqueue(fs_info, "endio-write", flags,
@@ -2327,7 +2323,7 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info)
 	      fs_info->delalloc_workers && fs_info->flush_workers &&
 	      fs_info->endio_workers && fs_info->endio_meta_workers &&
 	      fs_info->compressed_write_workers &&
-	      fs_info->endio_write_workers && fs_info->endio_raid56_workers &&
+	      fs_info->endio_write_workers &&
 	      fs_info->endio_freespace_worker && fs_info->rmw_workers &&
 	      fs_info->caching_workers && fs_info->fixup_workers &&
 	      fs_info->delayed_workers && fs_info->qgroup_rescan_workers &&

fs/btrfs/fs.h

@@ -532,7 +532,6 @@ struct btrfs_fs_info {
 	struct btrfs_workqueue *flush_workers;
 	struct workqueue_struct *endio_workers;
 	struct workqueue_struct *endio_meta_workers;
-	struct workqueue_struct *endio_raid56_workers;
 	struct workqueue_struct *rmw_workers;
 	struct workqueue_struct *compressed_write_workers;
 	struct btrfs_workqueue *endio_write_workers;

fs/btrfs/raid56.h

@@ -97,8 +97,6 @@ struct btrfs_raid_bio {
 
 	wait_queue_head_t io_wait;
 
-	struct work_struct end_io_work;
-
 	/* Bitmap to record which horizontal stripe has data */
 	unsigned long dbitmap;