Remove keybox from OEMCrypto ref

Merge from Widevine repo of http://go/wvgerrit/56526

This CL removes the test keybox from OEMCrypto reference code.

Test: unit tests
Bug: 76393338 split mock into ref and testbed
Change-Id: I4bf0eb777c6851191d0ac9ccf8e2b42c55c8f6b9

libwvdrmengine/oemcrypto/ref/src/oemcrypto_keybox_ref.h

@@ -33,9 +33,7 @@ class WvKeybox {
   bool InstallKeybox(const uint8_t* keybox, size_t keyBoxLength);
 
  private:
-  bool Prepare();
-
-  bool valid_;
+  bool loaded_;
   std::vector<uint8_t> device_id_;
   std::vector<uint8_t> device_key_;
   WvKeyboxKeyData key_data_;
@@ -43,11 +41,6 @@ class WvKeybox {
   uint8_t crc_[4];
 };
 
-class WvTestKeybox : public WvKeybox {
- public:
-  WvTestKeybox();
-};
-
 }  // namespace wvoec_ref
 
 #endif  // OEMCRYPTO_KEYBOX_REF_H_