iscsi-target: Drop legacy iscsi_target_tq.c logic

Now that iscsi_conn allocates new [rx,tx] threads using kthread.h
primitives on the fly, and kthread_stop() is called directly during
connection shutdown, it's time to go ahead and drop iscsi_target_tq.c
legacy code.

The use of multiple struct completion in iscsi_activate_thread_set()
has been proven to cause issues during repeated iser login/logout.

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

drivers/target/iscsi/iscsi_target_util.c

@@ -33,7 +33,6 @@
 #include "iscsi_target_erl1.h"
 #include "iscsi_target_erl2.h"
 #include "iscsi_target_tpg.h"
-#include "iscsi_target_tq.h"
 #include "iscsi_target_util.h"
 #include "iscsi_target.h"