refactor: Remove duplicate chain_sum function from basic_arithmetic.py

reasoning_gym/arithmetic/basic_arithmetic.py

@@ -143,39 +143,6 @@ class ArithmeticDataset:
         return expression, result
 
 
-def chain_sum(
-    min_terms: int = 2,
-    max_terms: int = 6,
-    min_digits: int = 1,
-    max_digits: int = 4,
-    allow_negation: bool = False,
-    seed: Optional[int] = None,
-    size: int = 500,
-) -> ChainSum:
-    """Create a ChainSum dataset with the given configuration.
-    
-    Args:
-        min_terms: Minimum number of terms in expressions
-        max_terms: Maximum number of terms in expressions
-        min_digits: Minimum number of digits in numbers
-        max_digits: Maximum number of digits in numbers
-        allow_negation: Whether to allow negative numbers
-        seed: Random seed for reproducibility
-        size: Virtual size of the dataset
-        
-    Returns:
-        ChainSum: Configured dataset instance
-    """
-    config = ChainSumConfig(
-        min_terms=min_terms,
-        max_terms=max_terms,
-        min_digits=min_digits,
-        max_digits=max_digits,
-        allow_negation=allow_negation,
-        seed=seed,
-        size=size,
-    )
-    return ChainSum(config)
 
     def __iter__(self):
         """Make the dataset iterable"""