cfg80211: remove WDS code

Remove all the code that was there to configure WDS interfaces,
now that there's no way to reach it anymore.

Link: https://lore.kernel.org/r/20201109105103.8f5b98e4068d.I5f5129041649ef2862b69683574bb3344743727b@changeid


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