Remove Celery and its related tasks

[dodo920306]

Summary

Remove Celery and its related tasks to simplify the project architecture

Changes

• Remove api_engine/celery.py configuration file
• Remove all Celery tasks under api/tasks/ directory
• Update requirements.txt to remove Celery-related dependencies

Motivation

Celery is no longer used in the current architecture. Removing it reduces project complexity and dependencies.

---

🤖 This PR description was generated with AI assistance (Claude, Anthropic).

[yeasy]

Why CI fails?

[dodo920306]

Why CI fails?

I don't actually know. I don't think I changed any thing that will cause the newman tests failed, but they failed.

[dodo920306]

Why CI fails?

@yeasy It now passed. Can you merge this please 🙏?

[dodo920306]

@yeasy Do we have to use GitHub Pages? If not, can we turn it off? It failed to be deployed on the main branch, and I don't have the permission to change the settings of it.

I don't think we actually need this since we already have Read the Docs.

[yeasy]

It seems defined in github actions.

[dodo920306]

It seems defined in github actions.

What? No way. Our GitHub Actions are extremely simple.
https://github.com/hyperledger-cello/cello/tree/main/.github/workflows

However, it seems like the original failed GitHub Page deployment task disappeared automatically, so I guess that is fine.

[yeasy]

Now it's closed.