tipc: remove zone_list member in struct publication

As a further consequence of the previous commits, we can also remove
the member 'zone_list 'in struct name_info and struct publication.
Instead, we now let the member cluster_list take over the role a
container of all publications of a given <type,lower, upper>.
We also remove the counters for the size of those lists, since
they don't serve any purpose.

Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>