Remove unused enable_snat attribute
Remove unused enable_snat attribute

This change removes from RouterInfo the enable_snat attribute which is
never used in neutron nor neutron-*aas.

Change-Id: Icc2f9b306b7119c9d041d208d26e846ed3381507

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