doc: Remove obsolete "reference label"
the feature was replaced in commit
@@ -30,13 +30,6 @@ exist:
* if you tag releases we recommend using the release tag (eg:
``v1.0.0``).
-Separately to the release version you can provide an optional reference label.
-That label can point to a human readable identifier that is a reference to
-that version that the time. As an example if you deploy a specific
-revision of the master branch you can set the version to the SHA of the
-commit but the reference to ``master``. This can help you figure out if a
-release happened from master, unstable or a feature branch.
-
Releases can also be auto created by different systems. For instance upon
uploading a sourcemap a release is automatically created. Likewise
releases are created by some clients when an event for a release comes in.
