intel_idle: remove stop/start critical timings

The start/stop_critical_timings are called from arch/x86/kernel/process.c
in the cpu_idle loop function.

Remove the ones in the cpuidle driver.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>