runtime: remove duplicate copyright notice

Change-Id: Ibe3ba6426cc6e683ff3712faf6119922d0f88b5a
Reviewed-on: https://go-review.googlesource.com/2680Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/os_linux_arm.go

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Copyright 2009 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 runtime
 
 import "unsafe"