From visual inspection of the code, MigrationSourceManager::commitChunkMetadataOnConfig does not check the command response for writeConcernStatus, nor does it send majority write concern in the command.
On the config server, ShardingCatalogManager::commitChunkMigration does not appear to include majority write concern in its final write. This was probably because we used to take a lock twice to nest and prevent yielding, which makes yielding to wait for replication impossible, in order to enforce serialization of commits. Now, however, we use a _kChunkOpLock to serialize operations, no longer taking locks. These kind of comments should also be removed: https://github.com/mongodb/mongo/blob/e37db69674486dff9fdac2b5ee41961a8805804b/src/mongo/s/catalog/sharding_catalog_manager_chunk_operations.cpp#L223-L225