rcu/nocb: Remove SEGCBLIST_KTHREAD_CB

This state excerpt from the (de-)offloading state machine was used to
implement an ad-hoc kthread parking of rcuo kthreads. This code has
been removed and therefore the related state can be erased as well.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>

include/linux/rcu_segcblist.h

@@ -186,9 +186,8 @@ struct rcu_cblist {
  */
 #define SEGCBLIST_ENABLED	BIT(0)
 #define SEGCBLIST_LOCKING	BIT(1)
-#define SEGCBLIST_KTHREAD_CB	BIT(2)
-#define SEGCBLIST_KTHREAD_GP	BIT(3)
-#define SEGCBLIST_OFFLOADED	BIT(4)
+#define SEGCBLIST_KTHREAD_GP	BIT(2)
+#define SEGCBLIST_OFFLOADED	BIT(3)
 
 struct rcu_segcblist {
 	struct rcu_head *head;