chore: update to latest (manylinux1) requirements.txt

[henryiii]

This pulls the latest requirements.txt from the manylinux1 branch upstream, since the main branch does not support Python 2 anymore.

PS: The main reason I need this is for pypa/build, which is missing from the current image. Xref: pypa/cibuildwheel#521

[asottile]

I'm confused, do we need this file at all? can we pull this straight from the primary image?

[henryiii]

Doesn't it get removed here? https://github.com/pypa/manylinux/blob/606ba6c7c4e007acf613292b6b18bd5c02573559/docker/Dockerfile#L158

Besides, the main image (2010, 2014, 2_24) no longer supports Python 2, so this has to come from the manylinux1 image, where Python 2 pins are still included (for PyPy2). This builds on the manylinux2010 image.

[asottile]

oh I guess that's true -- I wonder if we should drop pypy2 (even though pypy is ~indefinitely supported -- it's going to be increasingly difficult to maintain a set of working requirements)

[henryiii]

I'd recommend keeping it around for the moment here (I'm not recommending supporting pypy2 in pypa/manylinux#1099 ), since one benefit of this image is that it holds a lot of older PyPy's. However, as soon as it's actually a problem to maintain, I'd drop it. Totally not up to me, though. :)