iwlwifi: cfg: remove unnecessary cfg data in non-dvm devices

The max_data_size and max_inst_size values are only needed for DVM
devices.  Remove the assignment to those fields in 7000 and newer
families so we can also remove the otherwise unnecessary inclusion of
iwl-agn.h headers.

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