Now that we have the possibility to use the honor_labels configuration
there is no need for this specially treated annotation anymore.

git-subtree-dir: contrib/kube-prometheus
git-subtree-mainline: 050ca21276696c8603375c699513ec487301ed62
git-subtree-split: 81c0d2f4

These annotations made sense in pre v1.3.0 Prometheus releases, however,
with >=v1.3.0 and the Prometheus Operator these annotations are more
confusing then helpful.