rcu: Remove obsolete boost statistics for debugfs

The debugfs interface displayed statistics on RCU priority boosting,
but this interface has since been removed.  This commit therefore
removes the no-longer-used rcu_data structure's ->n_tasks_boosted,
->n_exp_boosts, and ->n_exp_boosts and their updates.

If this information proves necessary in the future, the corresponding
event traces will be added.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.h

@@ -146,12 +146,6 @@ struct rcu_node {
 				/*  boosting for this rcu_node structure. */
 	unsigned int boost_kthread_status;
 				/* State of boost_kthread_task for tracing. */
-	unsigned long n_tasks_boosted;
-				/* Total number of tasks boosted. */
-	unsigned long n_exp_boosts;
-				/* Number of tasks boosted for expedited GP. */
-	unsigned long n_normal_boosts;
-				/* Number of tasks boosted for normal GP. */
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */

kernel/rcu/tree_plugin.h

@@ -963,14 +963,10 @@ static int rcu_boost(struct rcu_node *rnp)
 	 * expedited grace period must boost all blocked tasks, including
 	 * those blocking the pre-existing normal grace period.
 	 */
-	if (rnp->exp_tasks != NULL) {
+	if (rnp->exp_tasks != NULL)
 		tb = rnp->exp_tasks;
-		rnp->n_exp_boosts++;
-	} else {
+	else
 		tb = rnp->boost_tasks;
-		rnp->n_normal_boosts++;
-	}
-	rnp->n_tasks_boosted++;
 
 	/*
 	 * We boost task t by manufacturing an rt_mutex that appears to