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)