init_task: Remove redundant INIT_TASK_RCU_TREE_PREEMPT() macro

Back in the dim distant past, the task_struct structure's RCU-related
fields optionally included those needed for CONFIG_RCU_BOOST, even in
CONFIG_PREEMPT_RCU builds.  The INIT_TASK_RCU_TREE_PREEMPT() macro was
used to provide initializers for those optional CONFIG_RCU_BOOST fields.
However, the CONFIG_RCU_BOOST fields are now included unconditionally
in CONFIG_PREEMPT_RCU builds, so there is no longer any need fro the
INIT_TASK_RCU_TREE_PREEMPT() macro.  This commit therefore removes it
in favor of initializing the ->rcu_blocked_node field directly in the
INIT_TASK_RCU_PREEMPT() macro.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/init_task.h

@@ -125,18 +125,12 @@ extern struct group_info init_groups;
 #define INIT_IDS
 #endif
 
-#ifdef CONFIG_PREEMPT_RCU
-#define INIT_TASK_RCU_TREE_PREEMPT()					\
-	.rcu_blocked_node = NULL,
-#else
-#define INIT_TASK_RCU_TREE_PREEMPT(tsk)
-#endif
 #ifdef CONFIG_PREEMPT_RCU
 #define INIT_TASK_RCU_PREEMPT(tsk)					\
 	.rcu_read_lock_nesting = 0,					\
 	.rcu_read_unlock_special.s = 0,					\
 	.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry),		\
-	INIT_TASK_RCU_TREE_PREEMPT()
+	.rcu_blocked_node = NULL,
 #else
 #define INIT_TASK_RCU_PREEMPT(tsk)
 #endif