* rpc: simplify the handling of JSON-RPC request and response IDs
Replace the ID wrapper interface with plain JSON. Internally, the client
libraries use only integer IDs, and the server does not care about the ID
structure apart from checking its validity.
Basic structure of this change:
- Remove the jsonrpcid interface and its helpers.
- Unexport the ID field of request and response.
- Add helpers for constructing requests and responses.
- Fix up usage and tests.