cpuidle: remove cpuidle_unregister_governor()

cpuidle_unregister_governor() and cpuidle_replace_governor() aren't
used anymore and can be removed. They were used by cpufreq governors
earlier, but since the governors can't be compiled as modules any
more, these two functions aren't necessary.

Suggested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/cpuidle/governor.txt

@@ -25,5 +25,4 @@ kernel configuration and platform will be selected by cpuidle.
 
 Interfaces:
 extern int cpuidle_register_governor(struct cpuidle_governor *gov);
-extern void cpuidle_unregister_governor(struct cpuidle_governor *gov);
 struct cpuidle_governor