Review sync method behaviour

[jamescalam]

There are some cases such as force-remote and force-local that seem to be behaving slightly oddly. For example where additional routes are maintained where they should be removed, etc — we sometimes see this in the tests with the Route 3 utterance.

We must also try and remove include_metadata parameter from sync methods. This was added to handle the weird sync behaviours in the tests but was intended as a bandaid solution until a full fix is possible.