cpuidle: unexport tick_nohz_get_sleep_length

This patch removes the unused
EXPORT_SYMBOL_GPL(tick_nohz_get_sleep_length),
which we no long user b/c we no longer build optional modules.

Signed-off-by: Adrian Bunk <[e-mail]>
Acked-by: Venkatesh Pallipadi <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Len Brown <[e-mail]>

kernel/time/tick-sched.c

···
 	return ts->sleep_length;
 }
 
-EXPORT_SYMBOL_GPL(tick_nohz_get_sleep_length);
-
 /**
  * nohz_restart_sched_tick - restart the idle tick from the idle task
  *