Inconsistent license infomation for asn1 and x509

[syvb]

The files in the asn1 and x509 directory are taken from the Go standard library, which is licensed under a BSD-style license. They have license headers that say:

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

But the license file in this repo has the Apache License, Version 2.0, which is not the BSD-style license referred to.

Either the correct license file should be added to those directories, or these file should be relicensed to Apache 2.0 by Google.