Add a clearer error message for MARC-ja.

JGLUE.py

@@ -241,6 +241,11 @@ class JGLUE(ds.GeneratorBasedBuilder):
             raise ValueError(f"Invalid config name: {self.config.name}")
 
     def __split_generators_marc_ja(self, dl_manager: ds.DownloadManager):
+        raise RuntimeError(
+            "The Amazon Review Dataset is currently no longer public. "
+            "For sentiment analysis, consider using the `llm-book/wrime-sentiment` dataset instead."
+        )
+        
         file_paths = dl_manager.download_and_extract(_URLS[self.config.name])
 
         filter_review_id_list = file_paths["filter_review_id_list"]