These are used to signal the start of the document in a stream of many
documents. As Ansible only supports one YAML document per file this is
unnecessary. About a third of our YAML documents already lacked these.

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