btrfs: remove unused BTRFS_FS_BARRIER flag

This is no longer used, the -o nobarrier is handled by
BTRFS_MOUNT_NOBARRIER.  Remove the flag.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -548,7 +548,6 @@ struct btrfs_swapfile_pin {
 bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr);
 
 enum {
-	BTRFS_FS_BARRIER,
 	BTRFS_FS_CLOSING_START,
 	BTRFS_FS_CLOSING_DONE,
 	BTRFS_FS_LOG_RECOVERING,

fs/btrfs/disk-io.c

@@ -2956,7 +2956,6 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 
 	extent_io_tree_init(fs_info, &fs_info->excluded_extents,
 			    IO_TREE_FS_EXCLUDED_EXTENTS, NULL);
-	set_bit(BTRFS_FS_BARRIER, &fs_info->flags);
 
 	mutex_init(&fs_info->ordered_operations_mutex);
 	mutex_init(&fs_info->tree_log_mutex);