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

[Roundup Robot]

Roundup Robot added the comment:

New changeset bb7e01b5d362 by Raymond Hettinger in branch '3.3':
Issue #17351: Modernize the pure Python property() example.
http://hg.python.org/cpython/rev/bb7e01b5d362

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