remove unused field for chat_template.default for DPO training (#2755) [skip ci]

* remove unused field for chat_template.default

"messages" field present in final dataset causes issues with DPO
training otherwise

* lint and fix tests for new return value

* remove unused field for chat_template.default

"messages" field present in final dataset causes issues with DPO
training otherwise

lint and fix tests for new return value

fix for updated expected fields for dpo

remove unused field for chat_template.default

"messages" field present in final dataset causes issues with DPO
training otherwise

fix test still expecting "messages" field

* chore: lint

---------

Co-authored-by: Wing Lian <wing@axolotl.ai>

tests/test_datasets.py

@@ -289,7 +289,10 @@ class TestDatasetPreparation:
         train_dataset, _ = load_prepare_preference_datasets(cfg)
 
         assert len(train_dataset) == 1800
-        assert "conversation" in train_dataset.features
+        assert "conversation" not in train_dataset.features
+        assert "chosen" in train_dataset.features
+        assert "rejected" in train_dataset.features
+        assert "prompt" in train_dataset.features
 
     @pytest.mark.skip(reason="TODO: fix hf hub offline to work with HF rate limits")
     @enable_hf_offline
@@ -348,7 +351,10 @@ class TestDatasetPreparation:
             train_dataset, _ = load_prepare_preference_datasets(cfg)
 
             assert len(train_dataset) == 1800
-            assert "conversation" in train_dataset.features
+            assert "conversation" not in train_dataset.features
+            assert "chosen" in train_dataset.features
+            assert "rejected" in train_dataset.features
+            assert "prompt" in train_dataset.features
 
     @enable_hf_offline
     @pytest.mark.skip("datasets bug with local datasets when offline")