Finalize backfill_bulk_import_trackers_project_id BBM

What does this MR do and why?

Finalize backfill_bulk_import_trackers_* BBMs

Addresses &11670

Following the re-queue and completion of !197155 (merged). Now is the time to finalize this batch background migration.

Batch Background Migration Completed Status

BBMs being part of last required stop (18.2)

As per (https://docs.gitlab.com/development/database/batched_background_migrations/#finalize-a-batched-background-migration);

We recommend that batched background migrations are finalized after all of the following conditions are met:

• The batched background migration is completed on GitLab.com
• The batched background migration was added in or before the last required stop. For example if 17.8 is a required stop and the migration was added in 17.7, the finalizing migration can be added in 17.9.

We can finalize these BBMs in 18.3.

References

• &11670
• !197155 (merged)

MR acceptance checklist

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