Revert change in label_join per @RichiH
Revert change in label_join per @RichiH

Signed-off-by: smedbergM <5534e1b47196d1be03b1221ad6d2f2aaa61996f3@gmail.com>

GoogleCloudPlatform/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus,keegancsmith/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus