[Twisted-Python] itervalues in pypi package

[Nathaniel Haggard]

When making a python3 virtualenv and installing twisted I get
t/i/process.py that has .itervalues() in it, but this was fixed 3 months
ago (https://twistedmatrix.com/trac/ticket/9933).

```
curl
https://files.pythonhosted.org/packages/c2/41/3f30da0f7025480eff8feb9ef0927c6db6bbbf6e64985cac77ee0210a903/Twisted-21.2.0.tar.gz
> t
tar xvzf t
grep itervalues Twisted-21.2.0/src/twisted/internet/process.py
        for p in self.pipes.itervalues():
        for p in self.pipes.itervalues():
```

Thanks,
Nate
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