That has nothing to do if the Authentication is done locally or over RADIUS.
Just disable the drop-down on the ASA:
asa# conf t
asa(config)# webvpn
asa(config-webvpn)# no tunnel-group-list enable
Just make sure that your users connect to the right tunnel-group. That can be the default-tunnel-group or be selected by the group-url:
tunnel-group VPN webvpn-attributes
group-url https://vpn.example.com/vpn enable