Update Galaxy repos config and drop support for Galaxy config repo

[natefoo]

Per the docs, config repos are really for site usage, not for repo providers:

The config repository is a very convenient method for updating the configuration on a lot of CernVM-FS clients at once. This also means that it is very easy to break configurations on a lot of clients at once. Also note that only one config repository may be used per client, and this is a technical limitation that is not expected to change. For these reasons, it makes the most sense to reserve the use of this feature for large groups of sites that share a common infrastructure with trusted people that maintain the configuration repository. In order to facilitate sharing of configurations between the infrastructures, a github repository has been set up. Infrastructure maintainers are invited to collaborate there.

[natefoo]

Reading that again now I'm not as convinced at my assertion - I think our config repo usage is actually exactly what it's intended for, this lets me (for example) change a key without having to get everyone with installed clients to update their keys manually.