[doc] reformat changes files headers
to remove the "what's new" phrasing and add the publication date instead.
Related to #4832808
# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s specific hooks and operations"""