Remove unused import: OrderedDict

Author: itholic

databricks/koalas/series.py

@@ -19,7 +19,7 @@
 """
 import re
 import inspect
-from collections import Iterable, OrderedDict
+from collections import Iterable
 from functools import partial, wraps
 from typing import Any, Generic, List, Optional, Tuple, TypeVar, Union