iwlwifi: remove chain noise calibration functions from 6000 family

redefine structures that contain function pointer for chain noise reset
and chain noise gain for the 6000 family since these are not needed.

Signed-off-by: Jay Sternberg <jay.e.sternberg@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>