Do not build PPC64le wheels

[hombit]

After GitHub Actions introduced ARM runners last month (adopted in #478), the PPC64le wheel build pipeline is the only one using QEMU emulation. QEMU emulation has problems right now, see #477, and it is x5 times slower to build a package under emulation than on a native platform:
https://github.com/light-curve/light-curve-python/actions/runs/12890119787/usage

I also believe that we have no PPC64le users; probably, I was the only one when I had access to NCSA's PPC HAL cluster.

That's why we are going to stop building PPC64le wheels and publish them to PyPI.