Not doing {% if matrix_admin %} checks in the YAML also fixes some issues
with indentation being incorrect sometimes.
This should be backward compatible, except for mautrix-signal's case
where `matrix_mautrix_signal_bridge_permissions` previously existed
as a string, not a dictionary. `tasks/validate_config.yml` will catch
the problem an even provide a quick fix.
This bridge doesn't support SQLite anyway, so it's not necessary
to carry around configuration fields and code for migration from SQLite
to Postgres. There's nothing to migrate.
This configuration is supposed to be kept clean and not reference variables defined in other roles.
`group_vars/matrix_servers` redefines these to hook our various roles together.
