google: Support deleting shared Google Drive files

gdata_documents_service_remove_entry_from_folder was earlier performing a PUT request for removing parent folders of a file, but Drive API disallows (it keeps atleast 1 parents) setting the "parents" field in PUT request to an empty array. Instead, a DELETE request needs to be used.

Relevant MR: libgdata!5 (merged) Fixes: #265 (moved)