iscsi-target: Drop left-over bogus iscsi_np->tpg_np

This patch drops the left-over iscsi_np->tpg_np pointer, now
that iser-target PI is able to dynamically allocate PI contexts
per I/O, instead of needing to determine support using a TPG
attribute with this bogus reference.

Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_core.h

@@ -790,7 +790,6 @@ struct iscsi_np {
 	void			*np_context;
 	struct iscsit_transport *np_transport;
 	struct list_head	np_list;
-	struct iscsi_tpg_np	*tpg_np;
 } ____cacheline_aligned;
 
 struct iscsi_tpg_np {

drivers/target/iscsi/iscsi_target_tpg.c

@@ -501,7 +501,6 @@ struct iscsi_tpg_np *iscsit_tpg_add_network_portal(
 	init_completion(&tpg_np->tpg_np_comp);
 	kref_init(&tpg_np->tpg_np_kref);
 	tpg_np->tpg_np		= np;
-	np->tpg_np		= tpg_np;
 	tpg_np->tpg		= tpg;
 
 	spin_lock(&tpg->tpg_np_lock);