dm: Remove unused declaration and empty definition "dm_zone_map_bio"

dm_zone_map_bio() has beed removed since commit f211268e ("dm: Use
the block layer zone append emulation"), remain the declaration unused in
header files. So, let's remove this unused declaration and empty
definition.

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>