Remove metadata merging; use only the latest document
We don't use that feature at all as far as I am aware.
I also find that it complicates any metadata handling (especially the validation I would like to add in the near future, #3965 (closed)), and probably does not match semantics intended by SWORD (merging occurs on PUT requests, as we don't implement PATCH)
Migrated from D7211 (view on Phabricator)