CI: Remove stub files from the repo

We only added these for platforms that were cross-compiling and couldn't build the stubs. That was only osx-arm64 on conda-forge.

Now, conda-forge have osx-arm64 runners, so we can generate the stubs at build time.

This makes development easier, as we no longer have to keep the stubs in sync.

We still keep the formatting improvements from the previous MR: !915 (merged)