Remove in-instance network policy configuration.

Network policy should be driven by API clients rather than in-instance
scripts, as using Heat to proxy the handover just adds an unnecessary
layer of indirection. We need to keep the logic for configuring ovs
within instances, just not the neutron net-create etc.

Change-Id: Iaee70ef5c9d1ff2a608e4ea64e766920bfba7f42