iwlwifi: remove references to 8000 B-step devices

We don't have any 8000 B-step right now, and there is no
firmware loading code for them anyway.
Further more, 9000 B-step devices will hit those code paths.
Remove code that was introduced only for 8000 B-step.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>