rcu/nocb: Remove obsolete nocb_cb_tail and nocb_cb_head fields

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree.h

@@ -194,8 +194,6 @@ struct rcu_data {
 
 	/* 5) Callback offloading. */
 #ifdef CONFIG_RCU_NOCB_CPU
-	struct rcu_head *nocb_cb_head;	/* CBs ready to invoke. */
-	struct rcu_head **nocb_cb_tail;
 	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
 	struct task_struct *nocb_gp_kthread;
 	raw_spinlock_t nocb_lock;	/* Guard following pair of fields. */

kernel/rcu/tree_plugin.h

@@ -1913,7 +1913,6 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
 {
 	init_swait_queue_head(&rdp->nocb_cb_wq);
 	init_swait_queue_head(&rdp->nocb_gp_wq);
-	rdp->nocb_cb_tail = &rdp->nocb_cb_head;
 	raw_spin_lock_init(&rdp->nocb_lock);
 	timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
 }