Revert "Apply bettertransformer by default for causallm (#605)"

This reverts commit 948f99d.

Author: eaidova

optimum/exporters/openvino/convert.py

@@ -293,7 +293,7 @@ def export_pytorch(
     logger.info(f"Using framework PyTorch: {torch.__version__}")
     output = Path(output)
 
-    if ensure_export_task_support_stateful(config.task):
+    if stateful:
         # Trigger bettertransformer together with stateful model because OpenVINO HW-dependent transformations expect
         # both of them are applied to demonstrate the best performance.
         # TODO: Consider applying bettertransformer regardless of stateful flag -- requires additional validation.