iwlwifi: remove redundant iwl9560_2ac_cfg struct

The iwl9560_2ac_cfg struct is used for PNJ devices and the
configuration is the same as iwl9260_2ac_cfg, so we can remove the
former to avoid redundancy.

Change-Id: I17ac1802f00bd80006930b922a9fc21df60e3c16
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>