cpuidle: menu governor - remove unused macro STDDEV_THRESH

STDDEV_THRESH was once defined and used in menu governor. But now its no longer
used anywhere. So removing the define.
Signed-off-by: Mohammad Merajul Islam Molla <meraj.enigma@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/governors/menu.c

@@ -35,7 +35,6 @@
 #define RESOLUTION 1024
 #define DECAY 8
 #define MAX_INTERESTING 50000
-#define STDDEV_THRESH 400
 
 
 /*