Fix godeps

Signed-off-by: Olivier Gambier <olivier@docker.com>

vendor/golang.org/x/net/context/ctxhttp/cancelreq.go

@@ -1,18 +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.
-
-// +build go1.5
-
-package ctxhttp
-
-import "net/http"
-
-func canceler(client *http.Client, req *http.Request) func() {
-	ch := make(chan struct{})
-	req.Cancel = ch
-
-	return func() {
-		close(ch)
-	}
-}