iwlwifi: remove unused parameters

parameters "len" is not used in both iwl_tx_queue_free() and
iwl_cmd_queue_free() functions

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>