Remove CreateCrossProjectPipelineWorker after revert

What does this MR do and why?

Note: This MR was reverted previously due to an incident. The fix was added as per the issue and the updated doc.

Original MR !118334 (merged)

Revert MR of the Original MR !118986 (merged)

Changelog:

Remove CreateCrossProjectPipelineWorker

CreateCrossProjectPipelineWorker has been replaced by CreateDownstreamPipelineWorker
in https://gitlab.com/gitlab-org/gitlab/-/issues/11081 and so the former has been
scheduled for removal.

Changelog: deprecated

Screenshots or screen recordings

Migration:

Rollback:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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