FWaaS plugin doesn't need to handle firewall rule del ops
FWaaS plugin doesn't need to handle firewall rule del ops

If firewall rule is attached to firewall policy, it would raise
FirewallRuleInUse excpetion in DB ops, else it is a pure DB delete ops.
So it is useless to handle delete_firewall_rule ops in fwaas plugin.
Closes-Bug: #1322076

Change-Id: I55a000d206f232c79b41230f526007f684db8f4f

openstack/neutron-fwaas,openstack/neutron-fwaas,citrix-openstack-build/neutron-fwaas,gaolichuang/neutron-fwaas,gaolichuang/neutron-fwaas,dougwig/x-neutron-fwaas