node: avoid double close resp.Body

[gzliudan]

The functions rpcRequest and batchRpcRequest call baseRpcRequest. And resp.Body will be closed in the function baseRpcRequest later by t.Cleanup:

func baseRpcRequest(t *testing.T, url, bodyStr string, extraHeaders ...string) *http.Response {
        // ......
	t.Cleanup(func() { resp.Body.Close() })
	return resp
}

[s1na]

LGTM

[lightclient]

Looks like Martin recommended using the t.Cleanup function to generally close the resp.Body across many uses, but there were a few from the original node refactor in #21105.