Remove duplicate import.

Co-authored-by: Mark McDonald <macd@google.com>

google/generativeai/text.py

@@ -17,7 +17,7 @@
 import dataclasses
 from collections.abc import Iterable, Sequence
 import itertools
-from typing import Iterable, overload, TypeVar
+from typing import overload, TypeVar
 
 import google.ai.generativelanguage as glm