Restructed reference root of trust (2/3 DRM Cert)

[ Merge of http://go/wvgerrit/115551 ]

This change is the second part of a three part change for restructing
the root of trust used by the reference implementation.

The use of RSA_shared_ptr has been replaced with the standard library
std::shared_ptr using the RsaPrivateKey wrapper class.  The
AuthenticationRoot class now uses this for the built-in DRM cert key.

RSA decryption and signature operations within the session context are
now performed the RsaPrivateKey class.  This has reduced the code size
and complexity within the reference and testbed, focusing their
implementation on key policy and less on mechanics.

Bug: 168544740
Bug: 135283522
Test: oemcrypto_unittests ce_cdm_tests
Change-Id: Ic743a529a9858f3182290d8bcf5e1633737b005b

libwvdrmengine/oemcrypto/ref/src/oemcrypto_rsa_key_shared.h

@@ -1,42 +0,0 @@
-// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
-// source code may only be used and distributed under the Widevine Master
-// License Agreement.
-//
-//  Reference implementation of OEMCrypto APIs
-//
-#ifndef OEMCRYPTO_RSA_KEY_SHARED_H_
-#define OEMCRYPTO_RSA_KEY_SHARED_H_
-
-#include <stdint.h>
-
-#include <openssl/rsa.h>
-
-namespace wvoec_ref {
-
-// Shared pointer with specialized destructor.  This pointer is only shared
-// from a CryptoEngine to a Session -- so we don't have to use full reference
-// counting.
-class RSA_shared_ptr {
- public:
-  RSA_shared_ptr() : rsa_key_(nullptr), key_owned_(false) {}
-  ~RSA_shared_ptr() { reset(); };
-  // Explicitly allow copy as share.
-  explicit RSA_shared_ptr(const RSA_shared_ptr& other) :
-      rsa_key_(other.rsa_key_), key_owned_(false) {}
-  RSA* get() { return rsa_key_; }
-  void reset();
-  bool LoadPkcs8RsaKey(const uint8_t* buffer, size_t length);
-
- private:
-  void operator=(const RSA_shared_ptr);  // disallow assign.
-
-  RSA* rsa_key_;
-  bool key_owned_;
-};
-
-// Log errors from BoringSSL.
-void dump_boringssl_error();
-
-}  // namespace wvoec_ref
-
-#endif  // OEMCRYPTO_RSA_KEY_SHARED_H_