Jsonrpc: clean up previous change

Jsonrpc: clean up previous change

* lisp/jsonrpc.el (jsonrpc-connection): Rework slot names.
(jsonrpc-connection-receive): Rework.
(jsonrpc--call-deferred): Fix typo.
(jsonrpc--process-sentinel)
(jsonrpc--remove): Use new slot names.
(jsonrpc--continue): Rework.
(jsonrpc--async-request-1): Rework.
(jsonrpc--event): Remember to remove :jsonrpc-json from
foreign-message
(jsonrpc--connection-receive): Revamp.
(jsonrpc--connection-send)
(jsonrpc--connection-reply): Rework.
(jsonrpc--log-event): Revamp.
(jsonrpc-continuation-count): Use new slot name.