cpuidle: Remove pointless stub

The cpuidle.h header is declaring a function with an empty stub
for the cpuidle disabled case, but that function is only called
by cpuidle governors which depend on cpuidle anyway.

In other words, the function is only called when cpuidle is enabled,
so there is no need for the stub.

Remove the pointless stub.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/cpuidle.h

@@ -271,13 +271,8 @@ struct cpuidle_governor {
 	void (*reflect)		(struct cpuidle_device *dev, int index);
 };
 
-#ifdef CONFIG_CPU_IDLE
 extern int cpuidle_register_governor(struct cpuidle_governor *gov);
 extern s64 cpuidle_governor_latency_req(unsigned int cpu);
-#else
-static inline int cpuidle_register_governor(struct cpuidle_governor *gov)
-{return 0;}
-#endif
 
 #define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter,			\
 				idx,					\