rcu: Remove redundant rcu_cpu_stall_suppress declaration

No point in having two identical rcu_cpu_stall_suppress declarations,
so remove the more obscure of the two.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

@@ -642,8 +642,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 
 #endif /* #ifdef CONFIG_SMP */
 
-int rcu_cpu_stall_suppress __read_mostly;
-
 static void record_gp_stall_check_time(struct rcu_state *rsp)
 {
 	rsp->gp_start = jiffies;