Synapse needs the database to be in C locale. Since v1.56.0, it refuses
to start when this is not the case, see [upgrade.md][1].

[1]: https://github.com/matrix-org/synapse/blob/v1.56.0/docs/upgrade.md#change-in-behaviour-for-postgresql-databases-with-unsafe-locale

Node's address lookup strips the scope ID from link-local IPv6
addresses, making them invalid and unable to be connected to.

We're getting hit with this since Node 17 because it now defaults to the
`verbatim` dns-result-order and this happens to return the link-local
IPv6 address for `matrix.archlinux.org` first.

Specify `ipv4first` so we return to Node 16's behavior.

This was a regression which has been fixed upstream.

This reverts commit 67e7677e.

We're no longer allowed to reserve formerly used namespaces.