iwlwifi: remove external reference for non-exist data structure

Number of data structure for 6000 series no longer in production, the
data structure already being removed; also need to remove the external
reference define in iwl-dev.h

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>