Remove deduplicate_process_commit_worker feature flag

What does this MR do and why?

Contributes to #420750 (closed)

The feature flag was enabled on GitLab.com and deduplication was tested. This feature flag is not needed anymore.

References

• Rollout of `deduplicate_process_commit_worker` (#420750 - closed)
• Investigate `ProcessCommitWorker` deduplicate s... (#553403 - closed)

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Related to #420750 (closed)