pkg/httputil: drop go1.4 tests

pkg/httputil/cancelreq.go

@@ -4,8 +4,6 @@
 
 // borrowed from golang/net/context/ctxhttp/cancelreq.go
 
-// +build go1.5
-
 // Package httputil provides HTTP utility functions.
 package httputil
 

pkg/httputil/cancelreq_go14.go

@@ -1,25 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// borrowed from golang/net/context/ctxhttp/cancelreq_go14.go
-
-// +build !go1.5
-
-package httputil
-
-import "net/http"
-
-type requestCanceler interface {
-	CancelRequest(req *http.Request)
-}
-
-func RequestCanceler(rt http.RoundTripper, req *http.Request) func() {
-	c, ok := rt.(requestCanceler)
-	if !ok {
-		return func() {}
-	}
-	return func() {
-		c.CancelRequest(req)
-	}
-}