702866b225
This:
1. Deletes XModuleDescriptorToXBlockMixin
2. Deletes `metadata_traslations` and `_translate()` from `XmlParserMixin`,
and all related implementations.
3. Removes translations of deprecated OLX attributes during import/export:
<old_attr> : <new_attr>
- 'slug' : 'url_name'
- 'name' : 'display_name'
- 'id' : 'discussion_id' (Discussion XBlock)
- 'for' : 'discussion_target' (Discussion XBlock)
- 'attempts' : 'max_attempts' (CAPA)
Minimal course for testing the handling of non-tree courses. The same html component occurs under more than one vertical.