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 <bunk@kernel.org>
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Len Brown <len.brown@intel.com>

kernel/time/tick-sched.c

@@ -320,8 +320,6 @@ ktime_t tick_nohz_get_sleep_length(void)
 	return ts->sleep_length;
 }
 
-EXPORT_SYMBOL_GPL(tick_nohz_get_sleep_length);
-
 /**
  * nohz_restart_sched_tick - restart the idle tick from the idle task
  *