wireless: remove cfg80211_reg_mutex

This mutex is wrong, we use cfg80211_drv_mutex (which should
possibly be renamed to just cfg80211_mutex) everywhere except
in one place, fix that and get rid of the extra mutex.

Also get rid of a spurious regulatory_requests list definition.

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