iwlwifi: 802.11n new framework structures preperation

This patch removes unnecessary or duplicate 802.11n data from structures
in the code, and prepares them for new mac80211's 802.11n framework

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>