net/tipc: Remove unused struct distr_queue_item

After commit 09b5678c("tipc: remove dead code in tipc_net and relatives"),
struct distr_queue_item is not used any more and can be removed as well.

Signed-off-by: Yuan Can <yuancan@huawei.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Link: https://lore.kernel.org/r/20220928085636.71749-1-yuancan@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>