Avoid setting OEMCrypto_Algorithm enum vars with invalid values

[ Merge of http://go/wvgerrit/106203 ]

CdmSigningAlgorithm are converted into OEMCrypto_Algorithm enums
before being passed as parameters to OEMCrypto generic crypto functions.
The OEMCrypto_Algorithm variables should never be set to values not
specified in the enum declaration.

These private methods have also been moved to the anonymous namespace.

Bug: 168774486
Test: WV unit/integration tests
Change-Id: Ie570a3cf4447b6c133076baa0909d562824c8e4a

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -325,14 +325,6 @@ class CryptoSession {
   CdmResponseType SelectKey(const std::string& key_id,
                             CdmCipherMode cipher_mode);
 
-  static const OEMCrypto_Algorithm kInvalidAlgorithm =
-      static_cast<OEMCrypto_Algorithm>(-1);
-
-  OEMCrypto_Algorithm GenericSigningAlgorithm(CdmSigningAlgorithm algorithm);
-  OEMCrypto_Algorithm GenericEncryptionAlgorithm(
-      CdmEncryptionAlgorithm algorithm);
-  size_t GenericEncryptionBlockSize(CdmEncryptionAlgorithm algorithm);
-
   // These methods fall back into each other in the order given, depending on
   // how much data they were given and how much data OEMCrypto can accept in one
   // call.
@@ -408,10 +400,6 @@ class CryptoSession {
 
   static bool IsInitialized();
 
-  // Constants
-  static const size_t kAes128BlockSize = 16;  // Block size for AES_CBC_128
-  static const size_t kSignatureSize = 32;    // size for HMAC-SHA256 signature
-
   // The locking methods above should be used in preference to taking these
   // mutexes directly. If code takes these manually and needs to take more
   // than one, it must *always* take them in the order they are defined here.