CI: Remove hydra files

[nomeata]

this fixes #2565 by removing the remaining files that are only there for
Hydra’s sake, and updates the docs to remove mention of hydra.

[nomeata]

I still see evaluation reports form hydra. Didn’t IDX disable them on August 30? @pikajude? (Or maybe they were removed from the jobset repo, but hydra wasn’t redeployed?)

We can still merge this PR and simply ignore the status until hydra stops reporting stuff.

[github-actions]

Comparing from c65020b to fa51e44:
The produced WebAssembly code seems to be completely unchanged.

[crusso]

I still see evaluation reports form hydra. Didn’t IDX disable them on August 30? @pikajude? (Or maybe they were removed from the jobset repo, but hydra wasn’t redeployed?)

We can still merge this PR and simply ignore the status until hydra stops reporting stuff.

I had a brief look at https://github.com/dfinity-lab/hydra-jobsets and it seems to still contain references to motoko and motoko PR jobs. Not sure how to fix that. Is the idea that we remove all references to motoko?

[nomeata]

Yes, hydra no longer needs to know about motoko

[crusso]

@pikajude do you want to purge motoko from https://github.com/dfinity-lab/hydra-jobsets or would you like me to have a go (though I know not what I am doing and will be flying blind).

[nomeata]

In any case someone from IDX will have to redeploy the hydra config, I think, which I assume Claudio won’t be able to do himself.

[nomeata]

Hydra is failing anyways, so we can merge this, I think. Maybe that’ll make hydra stop reporting statuses here.

[nomeata]

Is the hydra builder still used by Motoko in some form?