Settings: notification lights - fix for devices without leds

On devices that don't have notification leds, the preference
should be hidden in display settings. I adapted the commented
code for the new PreferenceScreen and removed unneeded commented
parts. Now the value of config_intrusiveNotificationLed is checked
and the preference is displayed accordingly.

Change-Id: Ia7834d1f415928d566b1ab8bc93c361c738487f2

Conflicts:
	src/com/android/settings/DisplaySettings.java