Removes dunder div (#39151)
Summary:
BC-breaking note:
If a user is using one of these dunders directly they will not longer be available. Users should update to Python3 compatible dunders.
Original PR note:
`__div__` (and `__idiv__` and `__rdiv__`) are no longer special dunders in Python3. This PR replaces them with the `__truediv__` (`__itrudediv__`, `__rtruediv__`) dunders, since we no longer support Python2.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39151
Differential Revision: D22075713
Pulled By: mruberry
fbshipit-source-id: d318b47b51f7cc4c3728b1606a34d81e49ba0fa1
