docker-ce: do not delete generated iptables by docker-ce

Deleting rules that docker has created is error-prone, because with
every update docker we have  to check if anything has changed.
Cleaning up the firewall rules is part of the docker and should and must be
cleaned up and handeled by them when the service is terminated.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>