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_usage_table_ref.h

@@ -88,10 +88,11 @@ class UsageTable {
   virtual ~UsageTable();
 
   OEMCryptoResult CreateNewUsageEntry(SessionContext* session,
-                                      UsageTableEntry** entry,
+                                      std::unique_ptr<UsageTableEntry>* entry,
                                       uint32_t* usage_entry_number);
   OEMCryptoResult LoadUsageEntry(SessionContext* session,
-                                 UsageTableEntry** entry, uint32_t index,
+                                 std::unique_ptr<UsageTableEntry>* entry,
+                                 uint32_t index,
                                  const std::vector<uint8_t>& buffer,
                                  ODK_ClockValues* clock_values);
   OEMCryptoResult UpdateUsageEntry(