Deleting a page and replacing with an xref evades the "deleted page" check

### Describe the bug

these two PRs didn't trigger an error for deleted pages:

https://github.com/elastic/docs-content/pull/2989
https://github.com/elastic/docs-content/pull/2811

both of them deleted a page, but added an equivalent xref in the sidebar. CI passed cleanly. when the PRs were merged, the pages 404'd

note: the crosslinks within the repo were already cleaned up. does the deleted page logic still trip if there are no incoming links? I want to test this but want to log this bug asap

### Expected behavior

you can't run or hide from the "deleted page with no redirect" error

### Steps to reproduce

_No response_

### Tooling

- [x] docs-builder
- [ ] migration tooling
- [ ] I'm not sure