Improvements

• #3900: Reduced duplicate logs and warnings when running rasa train.

Bugfixes

• #5972: Remove the clean_up_entities method from the DIETClassifier and CRFEntityExtractor as it let to incorrect
  entity predictions.
• #5976: Fix server crashes that occurred when Rasa Open Source pulls a model from a
  model server <server_fetch_from_server> and an exception was thrown during
  model loading (such as a domain with invalid YAML).