API 2.9: Remove document_version from meta object

[JuAlMan]

Using image docker.sunet.se/dc4eu/apigw:apiv28

The document_version attribute should be removed from the meta object as we already have top-level attribute document_data_version for that purpose when uploading a document.
This was also changed in the current API v29 specification.

To be discussed:
Returning top level document_data_version when requesting documents via /document, /document/collect_id, /document/list
if this information is not part of the meta object anymore.