timer: remove clockevents_unregister_notifier

I find a function(clockevents_unregister_notifier) which is not called by
anything in tree.

Signed-off-by: Miao Xie <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/clockchips.h

···
 extern void clockevents_set_mode(struct clock_event_device *dev,
 				 enum clock_event_mode mode);
 extern int clockevents_register_notifier(struct notifier_block *nb);
-extern void clockevents_unregister_notifier(struct notifier_block *nb);
 extern int clockevents_program_event(struct clock_event_device *dev,
 				     ktime_t expires, ktime_t now);
 

kernel/time/clockevents.c

···
 	return ret;
 }
 
-/**
- * clockevents_unregister_notifier - unregister a clock events change listener
- */
-void clockevents_unregister_notifier(struct notifier_block *nb)
-{
-	spin_lock(&clockevents_lock);
-	raw_notifier_chain_unregister(&clockevents_chain, nb);
-	spin_unlock(&clockevents_lock);
-}
-
 /*
  * Notify about a clock event change. Called with clockevents_lock
  * held.