gh-38821: let the category setup handle the ideals
This is removing the `ideal` methods in the old `Ring` and `Field`
classes, moving them to the category setup.
Also removing one custom `ideal` method in multiple polynomial rings.
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
URL: https://github.com/sagemath/sage/pull/38821
Reported by: Frédéric Chapoton
Reviewer(s): Frédéric Chapoton, Martin Rubey
