btrfs: replace: BTRFS_DEV_REPLACE_ITEM_STATE_x defines should go

The BTRFS_DEV_REPLACE_ITEM_STATE_x defines, as shown in [1], are
unused in both kernel and btrfs-progs (except for one instance of
BTRFS_DEV_REPLACE_ITEM_STATE_NEVER_STARTED in kernel).

[1]
btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED        2
btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED        3
btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED       4

Further these define-values are different form its counterpart
BTRFS_IOCTL_DEV_REPLACE_STATE_x series as shown in [2].

[2]
btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_SUSPENDED   2
btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_FINISHED    3
btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_CANCELED    4

So this patch deletes the BTRFS_DEV_REPLACE_ITEM_STATE_x altogether, and
one instance of BTRFS_DEV_REPLACE_ITEM_STATE_NEVER_STARTED is replaced
with BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED in the kernel.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>