AthenaCommon: Py3 fix for ChapPy

`builtins.file` is not available in Py3 and does not need an import in
Py2.

Control/AthenaCommon/python/ChapPy.py

@@ -32,7 +32,6 @@ def dump( buf, stdout = sys.stdout ):
     fname = None
     if isinstance(buf, str):
         fname = buf
-    from builtins import file
     if six.PY3:
         import io
         file = io.IOBase # noqa: F811