If the parameter being passed is an object then it can be passed as a
JSON string rather than using the `--json` flag which simplifies the
command line.
rclone rc operations/list fs=/tmp remote=test opt='{"showHash": true}'
Rather than
rclone rc operations/list --json '{"fs": "/tmp", "remote": "test", "opt": {"showHash": true}}'
This adds expire and unlink fields to the PublicLink interface.
This fixes up the affected backends and removes unlink parameters
where they are present.
