removing reference to Source metadata class in search index
{% for key, value in object.extra_metadata.items %}{{key}} {{value}} {% endfor %}
{% for format in object.metadata.formats.all %}{{ format.value }} {% endfor %}
{% for ident in object.metadata.identifiers.all %}{{ ident.value }} {% endfor %}
-{% for source in object.metadata.sources.all %}{{ source.derived_from }} {% endfor %}
{% for relation in object.metadata.relations.all %}{{ relation.value }} {% endfor %}
{{ object.verbose_name }}
{% for f in object.logical_files %} {{ f.get_discovery_content_type }} {% endfor %}
