collectd: remove libip4tc dependency

collectd: remove libip4tc dependency
Base collectd doesn't require libip4tc as stated in the collectd git:

* libiptc (optional)
For querying iptables counters
<http://netfilter.org/>

And libip4tc is already added as a dependency in the iptables plugin
because it needs it, so remove this dependency from the default collectd
to make it compatible with the new nftables firewall4 (by not selecting
any iptables components).

Signed-off-by: Tiago Gaspar <tiagogaspar8@gmail.com>