mac80211: remove SSID driver code

Remove the SSID from the driver API since now there is no
driver that requires knowing the SSID and I think it's
unlikely that any hardware design that does require the
SSID will play well with mac80211.

This also removes support for setting the SSID in master
mode which will require a patch to hostapd to not try.

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