chore(github): Switch to organization-wide Issue templates (#5622)

# Description

## Summary\*

Following noir-lang/.github#29, we can now pull
directly from the organization-wide Issue templates and simplify
templates to maintain.

This PR deletes the repo-specific Issue templates, so GitHub would then
automatically pull the org-wide templates.

## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

Preview the templates:
https://github.com/noir-lang-test/noir/issues/new/choose