[docs] [issue7340] Doc for sys.exc_info has warning that is no longer valid

[Serhiy Storchaka]

Changes by Serhiy Storchaka <storchaka at gmail.com>:


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keywords: +easy
versions: +Python 3.3, Python 3.4 -Python 3.1

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue7340>
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