lights: fix notification and attention lights

- Turn off attention light in pulse rather than
  just turning flashing off.  This was causing
  the LED to be left on for any HAL that obeys
  the concept of LIGHT_FLASH_NONE.  Most HALs
  will either treat this as OFF, or have special
  handling for the attention LED case where
  it was getting left on.
- Remove some unnecessary code in Light

Change-Id: I36292ae0d57e0454d7c9f1d3c909a87affeaf7d2