Don't need builtins defined in tox.ini
Don't need builtins defined in tox.ini

Now that I9db859ed6d595a621f2b4d09992d2312453a0b75 is upstreamed, we
don't need builtins defined in tox.ini

Change-Id: Ia559d3255f5eb6ee6a8e9b8a4adda8f9ce34bdc6

openstack/neutron-vpnaas,openstack/neutron-vpnaas