Revert slice(None) test

We need to order the slice(None) to comply with test from
pandas/tests/indexing/multiindex/test_slice.py
test_per_axis_per_level_doc_examples

Author: nrebena

pandas/core/indexes/multi.py

@@ -3045,7 +3045,7 @@ def _update_indexer(idxr, indexer=indexer):
             elif com.is_null_slice(k):
                 # empty slice
                 # index is given to conserve the order of this level
-                indexer = _update_indexer(None, indexer=indexer)
+                indexer = _update_indexer(Int64Index(np.arange(n)), indexer=indexer)
 
             elif isinstance(k, slice):
 

pandas/tests/indexes/multi/test_indexing.py

@@ -555,7 +555,3 @@ def test_multiindex_loc_order():
         [["Colorado", "Ohio", "Ohio"], ["Green", "Red", "Green"]]
     )
     tm.assert_index_equal(res.columns, exp_columns)
-
-    res = df.loc[(slice(None), [2, 1]), :]
-    exp_index = pd.MultiIndex.from_arrays([["a", "b", "a", "b"], [2, 2, 1, 1]])
-    tm.assert_index_equal(res.index, exp_index)