Documentation: ABI: make current_governer_ro as a candidate for removal

Since both current_governor and current_governor_ro co-exist under
/sys/devices/system/cpu/cpuidle/ file, and it's duplicate,
make current_governer_ro as a candidate for removal.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>