iwlwifi: remove unused clip_groups priv member

Remove clip_groups from priv and related structure.
This code is for 3945 only and was renamed to 4965 in
when code was split.
Also remove unused RATE definitions

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>