When creating {T257260} I realized that these config options are still used in various places in code (mainly tests and default settings) which is not ideal.
These references should all be removed so that we can safely unset these variables in production.
All code should be getting these things from entity sources, including tests.
Looking at `EntitySourceDefinitionsLegacyRepoSettingsParser` this probably is:
- [] entityNamespaces
- [] changesDatabase
- [] conceptBaseUri
- [] foreignRepositories
And for `EntitySourceDefinitionsLegacyClientSettingsParser`:
- [] foreignRepositories
- [] repositories
- [] repoDatabase
- [] entityNamespaces
- [] repoConceptBaseUri
The `repositories` old legacy thing: https://doc.wikimedia.org/Wikibase/master/php/md_docs_topics_options.html#autotoc_md370
The `foreignRepositories` old legacy thing: https://doc.wikimedia.org/Wikibase/master/php/md_docs_topics_options.html#foreignRepositories
The new entitysources thing: https://doc.wikimedia.org/Wikibase/master/php/md_docs_topics_entitysources.html
**Acceptance criteria:๐๏ธ๐**
[] Release notes are updated (as this is user facing back compat config that is being removed), including how to migrate from old settings to new settings.
[] References to the old configuration options are all removed
[] Back compat layer for the old config options are removed
[] Docs are updated