chore: address PR review comments

Author: shuoweil

bigframes/core/blocks.py

@@ -3477,11 +3477,7 @@ def _pd_index_to_array_value(
         row[offset_id] = row_offset
         rows.append(row)
 
-    import pyarrow as pa
-
     if not rows:
-        from bigframes.dtypes import bigframes_dtype_to_arrow_dtype
-
         dtypes_list = getattr(index, "dtypes", None)
         if dtypes_list is None:
             dtypes_list = (
@@ -3491,7 +3487,7 @@ def _pd_index_to_array_value(
         fields = []
         for col_id, dtype in zip(col_ids, dtypes_list):
             try:
-                pa_type = bigframes_dtype_to_arrow_dtype(dtype)
+                pa_type = bigframes.dtypes.bigframes_dtype_to_arrow_dtype(dtype)
             except Exception:
                 pa_type = pa.string()
             fields.append(pa.field(col_id, pa_type))

tests/system/small/test_dataframe.py

@@ -5915,18 +5915,6 @@ def test_to_gbq_obj_ref_persists(session):
     assert loaded_df["uris"].dtype == dtypes.OBJ_REF_DTYPE
 
 
-def test_dataframe_melt_multiindex(session):
-    # Tests that `melt` operations via count do not cause MultiIndex drops in Arrow
-    df = pd.DataFrame({"A": [1], "B": ["string"], "C": [3]})
-    df.columns = pd.MultiIndex.from_tuples(
-        [("Group1", "A"), ("Group2", "B"), ("Group1", "C")]
-    )
-    bdf = session.read_pandas(df)
-
-    count_df = bdf.count().to_pandas()
-    assert count_df.shape[0] == 3
-
-
 @pytest.mark.parametrize(
     ("col_names", "ignore_index"),
     [