rcu: Drop early GP request check from rcu_gp_kthread()

Now that grace-period requests use funnel locking and now that they
set ->gp_flags to RCU_GP_FLAG_INIT even when the RCU grace-period
kthread has not yet started, rcu_gp_kthread() no longer needs to check
need_any_future_gp() at startup time.  This commit therefore removes
this check.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: NNicholas Piggin <npiggin@gmail.com>

kernel/rcu/tree.c

@@ -2135,12 +2135,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
 	struct rcu_state *rsp = arg;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
-	/* Check for early-boot work. */
-	raw_spin_lock_irq_rcu_node(rnp);
-	if (need_any_future_gp(rnp))
-		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
-	raw_spin_unlock_irq_rcu_node(rnp);
-
 	rcu_bind_gp_kthread();
 	for (;;) {