hostap: remove unnecessary register of mgd iface in hostapd

In zephyr_hostapd_init, calls net_if_get_wifi_sap to get the SAP iface,
it means mgd iface of SAP type is registered before zephyr_hostapd_init.
Actually the mgd iface of SAP should be called in iface_api.init phase.
Therefore, remove unnecessary register of mgd iface in hostapd init.

Signed-off-by: Maochen Wang <maochen.wang@nxp.com>