oauth2/internal: remove duplicate package documentation

Fixes golang/go#15855

Change-Id: I71a532a95995fbbfd8a9acd75244537cd05f02f0
Reviewed-on: https://go-review.googlesource.com/66730
Reviewed-by: JBD <[email protected]>

Author: Tim Cooper

internal/doc.go

@@ -0,0 +1,6 @@
+// Copyright 2017 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 internal contains support packages for oauth2 package.
+package internal

internal/oauth2.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (

internal/oauth2_test.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (

internal/token.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (

internal/token_test.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (

internal/transport.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (