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

[github-actions]

It looks like this PR modifies one or more .asciidoc files. These files are being migrated to Markdown, and any changes merged now will be lost. See the migration guide for details.