iwlwifi: mvm: clean up NO_PSDU case

We now no longer have any special code in
iwl_mvm_pass_packet_to_mac80211(), so don't
need to pass NO_PSDU packets through it.
Stop doing so and clean up the code there.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>