mac80211: remove WDS-related code

Now that all the mac80211-based drivers have removed WDS code
and in particular the ability to advertise such devices, also
remove all the code related to WDS here.

Link: https://lore.kernel.org/r/20201109105103.38960c413d46.I3603c90a44562d847c39d15d5ff33d8c00df5834@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>