review use of "b" field in applyOps update operations in sharding_catalog_manager_chunk_operations.cpp

Some of the chunk operations rely on the applyOps command. Some of the generated update operations still set the b field to enable upserts. Setting the b field has no effect unless the alwaysUpsert option is set to false; " We should review the use of the b field in this code and remove it/replace the update with an insert where it is appropriate.