dm: Remove unused macro DM_ZONE_INVALID_WP_OFST

dm: Remove unused macro DM_ZONE_INVALID_WP_OFST

With the switch to using the zone append emulation of the block layer
zone write plugging, the macro DM_ZONE_INVALID_WP_OFST is no longer used
in dm-zone.c. Remove its definition.

Fixes: f211268ed1f9 ("dm: Use the block layer zone append emulation")
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://lore.kernel.org/r/20240611023639.89277-5-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>