timers: Remove unused inline funtion debug_timer_free()

There is no caller in tree, remove it.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200909134749.32300-1-yuehaibing@huawei.com

kernel/time/timer.c

@@ -732,11 +732,6 @@ static inline void debug_timer_deactivate(struct timer_list *timer)
 	debug_object_deactivate(timer, &timer_debug_descr);
 }
 
-static inline void debug_timer_free(struct timer_list *timer)
-{
-	debug_object_free(timer, &timer_debug_descr);
-}
-
 static inline void debug_timer_assert_init(struct timer_list *timer)
 {
 	debug_object_assert_init(timer, &timer_debug_descr);