iwlwifi: remove unused parameter from iwl_channel_info

Number of HT40 power parameters are not used; remove those from
iwl_channel_info data structure

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>