xtables-addons: remove not needed iptables install dependency for RTSP helpers

xtables-addons: remove not needed iptables install dependency for RTSP helpers

The RTSP conntrack and nat does not dependent on iptables, but only on
nf_conntrack and nf_nat. The RTSP conntrack module is used as a helper in
firewall4 [1]. Previously, it was not possible to install RTSP kernel module
without also installing the not needed iptables modules. However, as firewall4
is based on nftables and not on iptables, this dependency is not necessary.

[1] https://github.com/openwrt/firewall4/blob/master/root/usr/share/firewall4/helpers#L89

Signed-off-by: Florian Eckert <redacted>