Delete resources that go missing/are deleted on the remote
As per OpenAIRE-EUDAT-DMP-service-pilot#54, make sure that resouces that are deleted/marked as deleted on the remote is also deleted (removed) from the Eestore.
Clients that use data from the eestore needs to cache exactly the bits that have been used anyway, and might want to have a way to mark its local copies as being gone on the remote (by first checking if they still exist on the eestore).