delete unused import (#38252)

Author: arw2019

pandas/core/groupby/groupby.py

@@ -50,7 +50,7 @@ class providing the base-class of operations.
 from pandas.errors import AbstractMethodError
 from pandas.util._decorators import Appender, Substitution, cache_readonly, doc
 
-from pandas.core.dtypes.cast import maybe_cast_result, maybe_downcast_to_dtype
+from pandas.core.dtypes.cast import maybe_downcast_to_dtype
 from pandas.core.dtypes.common import (
     ensure_float,
     is_bool_dtype,