[docs] [issue27618] docs for threading.Lock claim it's a class (since 3.3), but it's not (and has never been, apparently)

[Cheryl Sabella]

Changes by Cheryl Sabella <chekat2 at gmail.com>:


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pull_requests: +1972

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27618>
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