Once featureCompatibilityVersion 3.4-specific behavior is removed, the allowUnsafeRenamesDuringInitialSync flag will no longer be necessary because all collections will have UUIDs and so renames during initial sync will no longer be unsafe. As part of SERVER-32741, the initial_sync_rename_collection_unsafe.js test will be removed. The allowUnsafeRenamesDuringInitialSync flag should be removed as well.