net/http: replace a statement in http.Error

[Guest-615695028]

In the Go function

func Error(w ResponseWriter, error string, code int)

, we can replace

fmt.Fprintln(w, error)

with

w.Write([]byte(error+"\n"))

to reduce stack occupation and improve speed.

[seankhliao]

unless there's a real world benchmark that shows an improvement, this would just be code churn