Remove deprecated fields from v9.x

[mjwolf]

Remove deprecated fields from the previous major release:

• process.parent.pgid
• process.pgid
• service.node.role
• service.origin.node.role
• service.target.node.role

---

• Have you signed the contributor license agreement? y
• Have you followed the contributor guidelines? y
• For proposing substantial changes or additions to the schema, have you reviewed the RFC process? n/a
• If submitting code/script changes, have you verified all tests pass locally using make test? y
• If submitting schema/fields updates, have you generated new artifacts by running make and committed those changes? y
• Is your pull request against main? Unless there is a good reason otherwise, we prefer pull requests against main and will backport as needed. y
• Have you added an entry to the CHANGELOG.next.md? y

[github-actions]

Documentation changes preview: https://ecs_bk_2410.docs-preview.app.elstc.co/diff