CLN: remove _recast_datetimelike_result (#38156)

Author: jbrockmendel

Diff for: pandas/core/groupby/generic.py

@@ -46,7 +46,6 @@
     is_integer_dtype,
     is_interval_dtype,
     is_numeric_dtype,
-    is_object_dtype,
     is_scalar,
     needs_i8_conversion,
 )
@@ -1283,7 +1282,7 @@ def _wrap_applied_output_series(
         # as we are stacking can easily have object dtypes here
         so = self._selected_obj
         if so.ndim == 2 and so.dtypes.apply(needs_i8_conversion).any():
-            result = _recast_datetimelike_result(result)
+            result = result._convert(datetime=True)
         else:
             result = result._convert(datetime=True)
 
@@ -1836,40 +1835,3 @@ def nunique(self, dropna: bool = True) -> DataFrame:
         return results
 
     boxplot = boxplot_frame_groupby
-
-
-def _recast_datetimelike_result(result: DataFrame) -> DataFrame:
-    """
-    If we have date/time like in the original, then coerce dates
-    as we are stacking can easily have object dtypes here.
-
-    Parameters
-    ----------
-    result : DataFrame
-
-    Returns
-    -------
-    DataFrame
-
-    Notes
-    -----
-    - Assumes Groupby._selected_obj has ndim==2 and at least one
-    datetimelike column
-    """
-    result = result.copy()
-
-    obj_cols = [
-        idx
-        for idx in range(len(result.columns))
-        if is_object_dtype(result.dtypes.iloc[idx])
-    ]
-
-    # See GH#26285
-    for n in obj_cols:
-        values = result.iloc[:, n].values
-        converted = lib.maybe_convert_objects(
-            values, convert_datetime=True, convert_timedelta=True
-        )
-
-        result.iloc[:, n] = converted
-    return result