Remove io.OpenWrapper, deprecated in Python 3.10

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Since Python 3.10, io.OpenWrapper is no longer needed: just use open(). See issue #87846 for the long rationale. I modified staticmethod() in Python 3.10, so a static method is now a callable object.

It was deprecated in 2 Python versions (3.10 and 3.11), so it can now be removed (PEP 387).

I'm writing a PR to remove it.

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Static methods were made callable in issue #87848. See also the python-dev thread: https://mail.python.org/archives/list/python-dev@python.org/thread/QZ7SFW3IW3S2C5RMRJZOOUFSHHUINNME/