chat/py-xmpppy: Update to 0.7.0

Note that xmpp.py has been removed; use xmpp-message instead.

pkgsrc changes:
Allow python 3 builds, now that it works with python 3.

Upstream changes:

2021-12-28 0.7.0
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- Documentation: Improve README and setup.py
- ``xmpp-message``: Evaluate return value from ``connection.auth()`` and
  croak when it fails
- ``xmpp-message``: Optionally read credentials from ``~/.xsend`` file
- Remove ``basic.py`` and ``xsend.py`` example programs

2021-12-28 0.6.5
================
- Python 3: Encoding fix for authentication (#52). Thanks, @D-L, @sumdog and @gdt!

2021-10-19 0.6.4
================
- Python 3: Fix handling of ``socket.error``/``OSError`` exceptions

(gdt)