diff --git a/vendor/golang.org/x/sync/singleflight/singleflight.go b/vendor/golang.org/x/sync/singleflight/singleflight.go
deleted file mode 100644
index 9a4f8d59e0..0000000000
--- a/vendor/golang.org/x/sync/singleflight/singleflight.go
+++ /dev/null
@@ -1,111 +0,0 @@
-// Copyright 2013 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.
-
-// Package singleflight provides a duplicate function call suppression
-// mechanism.
-package singleflight // import "golang.org/x/sync/singleflight"
-
-import "sync"
-
-// call is an in-flight or completed singleflight.Do call
-type call struct {
-	wg sync.WaitGroup
-
-	// These fields are written once before the WaitGroup is done
-	// and are only read after the WaitGroup is done.
-	val interface{}
-	err error
-
-	// These fields are read and written with the singleflight
-	// mutex held before the WaitGroup is done, and are read but
-	// not written after the WaitGroup is done.
-	dups  int
-	chans []chan<- Result
-}
-
-// Group represents a class of work and forms a namespace in
-// which units of work can be executed with duplicate suppression.
-type Group struct {
-	mu sync.Mutex       // protects m
-	m  map[string]*call // lazily initialized
-}
-
-// Result holds the results of Do, so they can be passed
-// on a channel.
-type Result struct {
-	Val    interface{}
-	Err    error
-	Shared bool
-}
-
-// Do executes and returns the results of the given function, making
-// sure that only one execution is in-flight for a given key at a
-// time. If a duplicate comes in, the duplicate caller waits for the
-// original to complete and receives the same results.
-// The return value shared indicates whether v was given to multiple callers.
-func (g *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, err error, shared bool) {
-	g.mu.Lock()
-	if g.m == nil {
-		g.m = make(map[string]*call)
-	}
-	if c, ok := g.m[key]; ok {
-		c.dups++
-		g.mu.Unlock()
-		c.wg.Wait()
-		return c.val, c.err, true
-	}
-	c := new(call)
-	c.wg.Add(1)
-	g.m[key] = c
-	g.mu.Unlock()
-
-	g.doCall(c, key, fn)
-	return c.val, c.err, c.dups > 0
-}
-
-// DoChan is like Do but returns a channel that will receive the
-// results when they are ready.
-func (g *Group) DoChan(key string, fn func() (interface{}, error)) <-chan Result {
-	ch := make(chan Result, 1)
-	g.mu.Lock()
-	if g.m == nil {
-		g.m = make(map[string]*call)
-	}
-	if c, ok := g.m[key]; ok {
-		c.dups++
-		c.chans = append(c.chans, ch)
-		g.mu.Unlock()
-		return ch
-	}
-	c := &call{chans: []chan<- Result{ch}}
-	c.wg.Add(1)
-	g.m[key] = c
-	g.mu.Unlock()
-
-	go g.doCall(c, key, fn)
-
-	return ch
-}
-
-// doCall handles the single call for a key.
-func (g *Group) doCall(c *call, key string, fn func() (interface{}, error)) {
-	c.val, c.err = fn()
-	c.wg.Done()
-
-	g.mu.Lock()
-	delete(g.m, key)
-	for _, ch := range c.chans {
-		ch <- Result{c.val, c.err, c.dups > 0}
-	}
-	g.mu.Unlock()
-}
-
-// Forget tells the singleflight to forget about a key.  Future calls
-// to Do for this key will call the function rather than waiting for
-// an earlier call to complete.
-func (g *Group) Forget(key string) {
-	g.mu.Lock()
-	delete(g.m, key)
-	g.mu.Unlock()
-}