Remove JSON-RPC parse error result on server entry point

[tomaka]

The JSON-RPC spec mentions that

If there was an error in detecting the id in the Request object (e.g. Parse error/Invalid Request), it MUST be Null.

Given that there exists a mechanism for that situation, I think that it is more appropriate to use that mechanism to notify the JSON-RPC client of a parsing error rather than return a Result which is difficult to handle.

[tomaka]

The first step is to change the mechanism where large requests return an error. Instead, they should generate an erroneous JSON-RPC response.