Currently, when annotating a local PDF, the `file://` URL will be submitted to the server.
It is not appropriate to submit local file paths to the server.
Since entries in document.link should be URIs, omit the URL in the case of local files.

https://trello.com/c/K8t2kl9m/331-don-t-save-file-urls-in-document-metadata
53725fd