Use unique_ptr in oemcrypto ref

Merge from Widevine repo of http://go/wvgerrit/95945

The reference oemcrypto and testbed still use old style pointers, even
though we now require a more modern C++ compiler. Updated a few places
where smart pointer would be appropriate.

Bug: 141393616
Test: Ran unit tests
Change-Id: I8b1e155bce241075928e373478d6f8e1001233f9

libwvdrmengine/oemcrypto/ref/src/oemcrypto_session.h

@@ -267,7 +267,7 @@ class SessionContext {
   std::vector<uint8_t> encryption_key_;
   std::vector<uint8_t> session_key_;
   const Key* current_content_key_;
-  SessionContextKeys* session_keys_;
+  std::unique_ptr<SessionContextKeys> session_keys_;
   ODK_NonceValues nonce_values_;
   uint8_t license_request_hash_[ODK_SHA256_HASH_SIZE];
   RSA_shared_ptr rsa_key_;
@@ -275,7 +275,7 @@ class SessionContext {
   bool decrypt_started_;      // If the license has been used in this session.
   ODK_TimerLimits timer_limits_;
   ODK_ClockValues clock_values_;
-  UsageTableEntry* usage_entry_;
+  std::unique_ptr<UsageTableEntry> usage_entry_;
   SRMVersionStatus srm_requirements_status_;
   enum UsageEntryStatus {
     kNoUsageEntry,      // No entry loaded for this session.