time: remove obsolete declaration

The function, timekeeping_leap_insert, was removed in commit
6b43ae8aSigned-off-by: NRichard Cochran <richardcochran@gmail.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>

include/linux/time.h

@@ -167,7 +167,6 @@ extern void get_monotonic_boottime(struct timespec *ts);
 extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
 extern int timekeeping_valid_for_hres(void);
 extern u64 timekeeping_max_deferment(void);
-extern void timekeeping_leap_insert(int leapsecond);
 extern int timekeeping_inject_offset(struct timespec *ts);
 
 struct tms;