More aggressive filtering of excluded keys

Our approvals have a lot of ID arrays, which can't be filtered out using `excluded_json_keys`. This means we end up having to update more approvals files than should be necessary, when we make a simple change to a spec.

This PR tweaks the filtering so we filter out whole arrays (in addition to simple values) if a key matches `excluded_json_keys`.

It may be too aggressive for general use, so not sure if we'll want to push this upstream. But it'll definitely save us time.