wifi: mac80211: Drop stations iterator where the iterator function may sleep

wifi: mac80211: Drop stations iterator where the iterator function may sleep

This reverts commit acb99b9b2a08f ("mac80211: Add stations iterator
where the iterator function may sleep"). A different approach was found
for the rtw88 driver where most of the problematic locks were converted
to a driver-local mutex. Drop ieee80211_iterate_stations() because there
are no users of that function.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20221226191609.2934234-1-martin.blumenstingl@googlemail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>