Remove the unused power field from struct struct acpi_processor_cx.

[rjw: Modified changelog.]
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>