sched: kill unused scheduler decl.

I noticed this while making investigations into the tbench
regressions.  Please apply.

sched: Remove hrtick_resched() extern decl.

This function was removed by 31656519
("sched, x86: clean up hrtick implementation").
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -287,7 +287,6 @@ extern void trap_init(void);
 extern void account_process_tick(struct task_struct *task, int user);
 extern void update_process_times(int user);
 extern void scheduler_tick(void);
-extern void hrtick_resched(void);
 
 extern void sched_show_task(struct task_struct *p);