[CI] Revert setuptools CI Fix as the Failing Pipelines are Deprecated

[dg845]

What does this PR do?

Follow-up to #13129 and #13132 which maybe finally fixes the ModuleNotFoundError: No module named 'pkg_resources' CI error.

I think the previous fix didn't work because I assumed the error was triggered when installing the packages with the issue (such as k-diffusion), but I think the error actually happens at runtime when we try to import from the packages. This is because the clip-anytorch dependency of k-diffusion will attempt to explicitly import pkg_resources in setup.py:

https://github.com/rom1504/CLIP/blob/4610075309864ea7aaec976c58ccd69048b64c1e/setup.py#L3

So I think the solution is to pin setuptools to a version which still has pkg_resources so that the import succeeds.

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@sayakpaul
@DN6

[sayakpaul]

What a bummer! Is k_diffusion still used?

Should we consider fully deprecating it? @DN6

[dg845]

Ran the pr_tests_gpu.yml workflow manually (https://github.com/huggingface/diffusers/actions/runs/22047985704) and it looks like the issue is fixed: https://github.com/huggingface/diffusers/actions/runs/22047985704/job/63700281914

Is k_diffusion still used?

From a previous CI run with the error (https://github.com/huggingface/diffusers/actions/runs/21981663925/job/63505654736?pr=12524) it looks like it's still being used in diffusers.pipelines.stable_diffusion_k_diffusion.pipeline_stable_diffusion_k_diffusion.

[sayakpaul]

We should consider deprecating it and removing it from testing IMO like these:
https://huggingface.co/docs/diffusers/main/en/api/pipelines/attend_and_excite

[DN6]

diffusers/src/diffusers/pipelines/stable_diffusion_k_diffusion/pipeline_stable_diffusion_xl_k_diffusion.py

Line 86 in b0dc51d

DeprecatedPipelineMixin,

The pipelines are deprecated. Let's remove it. Opened a PR #13152