Drop DataSource handling

Closes #29 (closed)

• Removes arkindex_worker.worker.MANUAL_SLUG
  • No workers affected in teklia/workers
• Removes ElementsWorker.get_ml_result_slug
  • Affects generic_exporter (here, here, here, here)
  • Affects horae_exporter (here and here)
  • Affects balsac_exporter (here, here and here)

arkindex_worker/worker/version.py

@@ -23,7 +23,7 @@ class WorkerVersionMixin(object):
         Gets the worker version slug from cache if possible, otherwise makes an API request.
         Returns None if there is no associated worker version.
 
-        :type ml_result: Element, classification or transcription
+        :type worker_version_id: A worker version UUID
         """
         worker_version = self.get_worker_version(worker_version_id)
         return worker_version["worker"]["slug"]