WPS ER: Fix segfault in some selected registrar change cases

WPS ER: Fix segfault in some selected registrar change cases

Commit 628d54639a90f779fd5c98c31e049638de56b17e introduced number
of new WPS related ctrl_iface messages to hostapd. Some of these
were for ER events which do not make any sense to hostapd that
cannot operate as an ER. The WPS_EV_ER_SET_SELECTED_REGISTRAR one
from wps_registrar_sel_registrar_changed_event() was especially
problematic since it can cause wpa_supplicant ER code segfault due
to missing event data.

Revert all the ER specific changes from commit
628d54639a90f779fd5c98c31e049638de56b17e to get rid of the segfault
and undesired extra code in hostapd.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>