Core routers shouldn't need to originate prefixes

[bswinnerton]

Ideally we'd be able to leave out the originations key in the configurations of Core routers:

https://github.com/neptune-networks/peering/blob/0befb585b5ab437a99ca55bf9e40a9be11969f64/config/router.fqdn.example.yml#L67-L72

But they are currently powering things like:

https://github.com/neptune-networks/peering/blob/0befb585b5ab437a99ca55bf9e40a9be11969f64/templates/bird.conf.erb#L7-L21

Which are later used in:

https://github.com/neptune-networks/peering/blob/0befb585b5ab437a99ca55bf9e40a9be11969f64/templates/bird.conf.erb#L194-L210

And:

https://github.com/neptune-networks/peering/blob/0befb585b5ab437a99ca55bf9e40a9be11969f64/templates/bird.conf.erb#L212-L218

Perhaps we can separate the idea of "originations" from "IPs that are ours". The main goal here being that we are able to filter out any prefixes by customers who peer with core routers that may accidentally announce our own prefixes.