Delete orphaned ci_runner_machines records on self-managed

What does this MR do and why?

This MR adds a batched migration to delete orphaned ci_runner_machines records on self-managed, in the same way that they were deleted in .com when the table was still called ci_runner_machines_687967fa8a.

Changelog: other

note: It is advised to review this MR commit-by-commit.

References

• Re-introduce migration to delete orphaned ci_ru... (#530611 - closed)
• Delete DeleteOrphanedPartitionedCiRunnerMachine... (#504282 - closed)
• Remove orphaned managers from ci_runner_machine... (!172422 - merged)
• Remove orphaned managers from .com ci_runner_ma... (!176702 - merged)
• No-op ci_runner_machines_687967fa8a batched mig... (!185296 - merged)

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.