tipc: remove unused tipc_group_size

After commit eb929a91b213 ("tipc: improve poll() for group member socket"),
it is no longer used.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/group.c

@@ -159,11 +159,6 @@ u32 tipc_group_exclude(struct tipc_group *grp)
 	return 0;
 }
 
-int tipc_group_size(struct tipc_group *grp)
-{
-	return grp->member_cnt;
-}
-
 struct tipc_group *tipc_group_create(struct net *net, u32 portid,
 				     struct tipc_group_req *mreq,
 				     bool *group_is_open)