Remove iptables related code.

[axel7born]

What this PR does / why we need it:
This PR removes the code for the optional creation of iptables rules and the --setup-iptables flag. To our knowledge, this code is not being used and is not necessary, so we have decided to discontinue maintaining the iptables-related code.

Since we are also removing the associated flag, this constitutes a breaking change. Therefore, along with the image update, it is crucial to ensure that the --setup-iptables flag is no longer in use.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Remove the optional creation of iptables rules and the flag`--setup-iptables`.

[ScheererJ]

Thanks for the big simplification. I have just a minor change request.

[ScheererJ]

Suggested change

	err := c.netManager.RemoveIPAddress()
	if c.params.SetupIptables {
	for _, rule := range c.iptablesRules {
	exists := true
	for exists {
	err := c.iptables.DeleteRule(rule.table, rule.chain, rule.args...)
	if err != nil {
	klog.Errorf("Error deleting iptables rule %v - %s", rule, err)
	}
	exists, _ = c.iptables.EnsureRule(utiliptables.Prepend, rule.table, rule.chain, rule.args...)
	}
	// Delete the rule one last time since EnsureRule creates the rule if it doesn't exist
	err := c.iptables.DeleteRule(rule.table, rule.chain, rule.args...)
	if err != nil {
	klog.Errorf("Error deleting iptables rule %v - %s", rule, err)
	}
	}
	}
	return err
	return c.netManager.RemoveIPAddress()

[ScheererJ]

/lgtm