Remove gw_port expire call
Remove gw_port expire call

This was initially added as part of the patch here:
I09e8a694cdff7f64a642a39b45cbd12422132806
However, it doesn't serve a purpose anymore because nothing
references the gateway port DB object before it is deleted.

Closes-Bug: #1716243
Change-Id: I87b614f8aef73aab8b5dd8217c99db1fe3ade742

openstack/neutron,mahak/neutron,huntxu/neutron,eayunstack/neutron,openstack/neutron,noironetworks/neutron,noironetworks/neutron,openstack/neutron,mahak/neutron,huntxu/neutron,eayunstack/neutron,mahak/neutron