Replace godep with dep

vendor/golang.org/x/oauth2/client_appengine.go

@@ -1,25 +0,0 @@
-// Copyright 2014 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 appengine
-
-// App Engine hooks.
-
-package oauth2
-
-import (
-	"net/http"
-
-	"golang.org/x/net/context"
-	"golang.org/x/oauth2/internal"
-	"google.golang.org/appengine/urlfetch"
-)
-
-func init() {
-	internal.RegisterContextClientFunc(contextClientAppEngine)
-}
-
-func contextClientAppEngine(ctx context.Context) (*http.Client, error) {
-	return urlfetch.Client(ctx), nil
-}