[docs] [issue17351] Fixed python3 descriptor documentation example + removal of explicit "object" inheritance in docs

[Ned Batchelder]

Ned Batchelder added the comment:

Why is it important to remove subclassing object?  Isn't it still good form to mention object as a base class.

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nosy: +nedbat

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17351>
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