Remove superflous comment about interning of unicode dict keys on Python2. The...

Remove superflous comment about interning of unicode dict keys on Python2. The existing behaviour matches the C implementation.

persistent/persistence.py

@@ -339,12 +339,6 @@ class Persistent(object):
             for k, v in inst_dict.items():
                 # Normally the keys for instance attributes are interned.
                 # Do that here, but only if it is possible to do so.
-
-                # TODO: On Python 2 codebases that straddle Python3,
-                # and use 'from __future__ import unicode_literals' it's not
-                # unheard of to have unicode objects in the __dict__ by accident.
-                # Should we watch for that and attempt to encode it so it can be
-                # interned?
                 idict[intern(k) if type(k) is str else k] = v
         slotnames = self._slotnames()
         if slotnames: