Remove old-division check from .pylintrc

Pylinyt documentation says: "This message can’t be emitted when using
Python >= 3.0." but we are using Python 3.7 and it stills present,
apparently because of a bug in pylint. See also:

https://docs.pylint.org/en/1.6.0/features.html
pylint-dev/pylint#3039

.pylintrc

@@ -309,7 +309,6 @@ enable=print-statement,
        delslice-method,
        getslice-method,
        setslice-method,
-       old-division,
        dict-iter-method,
        dict-view-method,
        next-method-called,