[12.3 backport] VersionsCleaner script runs non-document nodes, produces IndexOutOfBoundsException

The versions cleaner script has as query //element(*, mix:versionable) so it selects not only documents but also nodes below /hippo:configuration and /hst:hst. If that is not the intent (?), we can select more narrowly.

Also it produces "java.lang.IndexOutOfBoundsException: Index: 0, Size: 0" if there is nothing to remove but still remove(0) is called.

See [^VersionsCleaner.log] on an archetype Hippo 12.2 project.