MIST-214 Don't add the RPC wrapper to the request JSON for DoRaw

The endpoints DoRaw is going to be calling aren't going to be registered with the RPC service and therefore aren't going to be looking for the RPC wrapper around the request. (e.g. snapshot download)
It's unnecessary and means that the raw/non-rpc handlers (e.g. /snapshots/download in mistify-agent-image) just have to care about unmarshalling the actual request json.