[PATCH] mac80211: kill PRISM2_PARAM_CLEAR_KEYS

Not used anywhere, hence dead code. wpa_supplicant has its
own clear_keys routine.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Jiri Benc <jbenc@suse.cz>
Signed-off-by: John W. Linville <linville@tuxdriver.com>