Remove experimental non-AP STA code from hostapd

Remove experimental non-AP STA code from hostapd

This was used to allow hostapd to associate as a non-AP STA to another
AP one the same channel while still acting as an AP with the Host AP
driver. This was very experimental and did not work with all firmware
versions. Nowadays, much better way of doing this is to use mac80211
virtual non-AP STA interface. As such, this experimental code can be
removed from hostapd to reduce the code size and make MLME code easier
to understand since it is now only handling AP functionality.