Issue 33813: Update overdue 'Deprecated ... removed in 3.x' messages

Reported on python-list by Vincent Vande Vivre.
"""
In Python-3.7.0b5 we can find at the end of html/parser.py:
    def unescape(self, s):
        warnings.warn('The unescape method is deprecated and will be removed '
                      'in 3.5, use html.unescape() instead.',
                      DeprecationWarning, stacklevel=2)
        return unescape(s)
"""
At minimum, /3.5/3.8 or after/  Since we often do not remove when we say we will, perhaps 'or after' should be routine.