Hard-coded route `fe80::8` in vpnc-script-win.js

For some reason, fe80::8 is hard-coded router address in vpnc-script-win.js: https://gitlab.com/openconnect/vpnc-scripts/-/blob/master/vpnc-script-win.js#L158-187

In other scripts, fe80::8 is not hard-coded. I propose to remove this addresses from vpnc-script-win.js.