block/nbd: don't touch s->sioc in nbd_teardown_connection()

Negotiation during reconnect is now done in a thread, and s->sioc is
not available during negotiation. Negotiation in thread will be
cancelled by nbd_client_connection_release() called from
nbd_clear_bdrvstate().  So, we don't need this code chunk anymore.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210610100802.5888-25-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/nbd.c

@@ -280,10 +280,6 @@ static void nbd_teardown_connection(BlockDriverState *bs)
     if (s->ioc) {
         /* finish any pending coroutines */
         qio_channel_shutdown(s->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
-    } else if (s->sioc) {
-        /* abort negotiation */
-        qio_channel_shutdown(QIO_CHANNEL(s->sioc), QIO_CHANNEL_SHUTDOWN_BOTH,
-                             NULL);
     }
 
     s->state = NBD_CLIENT_QUIT;