firewall: Drop legacy rules for PPPoE/PPTP

firewall: Drop legacy rules for PPPoE/PPTP

These rules where created to permit any local traffic to the firewall
when using a PPP connection that utilised Ethernet as transport.

This is however nonsensical and a security issue for any other
connection methods that call the RED interface "red0" and use PPP (e.g.
QMI).

Since PPPoE packets do not flow through iptables, these rules can be
dropped safely. We do not know whether PPTP works at all these days.

Fixes: #13088 - firewall: INPUT accepts all packets when using QMI for dial-in
Tested-by: Stefan Schantl <stefan.schantl@ipfire.org>
Tested-by: Arne Fitzenreiter <arne_f@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>