net/rpc/jsonrpc: remove unused serverCodec.resp field

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/10458045

src/pkg/net/rpc/jsonrpc/server.go

@@ -20,8 +20,7 @@ type serverCodec struct {
 	c   io.Closer
 
 	// temporary work space
-	req  serverRequest
-	resp serverResponse
+	req serverRequest
 
 	// JSON-RPC clients can use arbitrary json values as request IDs.
 	// Package rpc expects uint64 request IDs.