Remove poptorch/pea

[thecharlieblake]

pip install git+https://github.com/graphcore-research/unit-scaling.git

currently fails with:

× Encountered error while trying to install package.
╰─> poptorch-experimental-addons

I think because it requires our SDK to be available - which we clearly don't want! Easiest solution for now is just to remove the poptorch/pea stuff in the codebase. It's only a few lines of code. We can find a way to add this back in at a later date and fix the issue properly if needs be.

[DouglasOrr]

Would it be enough just to move poptorch-experimental-addons to a requirements-ipu.txt file? You already have the try... except that should make the code itself work without poptorch/pea (I think?)