Remove dead helpers

test/test_serialization.py

@@ -8,7 +8,6 @@ import test_regression
 import tempfile
 import pickle
 import mmap
-import sys
 
 this_dir = os.path.dirname(__file__)
 
@@ -27,10 +26,6 @@ def test_roundtrip_bytes(all_types):
         test_regression.check_all_types(msg)
 
 
-@pytest.mark.skipif(
-    sys.version_info[0] < 3,
-    reason="mmap doesn't implement the buffer interface under python 2.",
-)
 def test_roundtrip_bytes_mmap(all_types):
     msg = all_types.TestAllTypes.new_message()
     test_regression.init_all_types(msg)