Fix bug in LfsObject.replicables_for_current_secondary

What does this MR do?

LfsObject.replicables_for_current_secondary was refactored as part of !56286 (merged). A bug was introduced that caused it to include duplicate results when selective sync was enabled since we were including the results twice. This MR makes sure we only include selective sync results once

Does this MR meet the acceptance criteria?

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