Use 128 bit AES for key control block

Merge from Widevine repo of http://go/wvgerrit/49805

This aligns the oemcrypto reference code and unit tests to match the
API design doc: http://go/oemcrypto

bug: 79375509
test: unit tests pass
Change-Id: I13761a7384a17e99d88e61aaf80b4a22941fd172

libwvdrmengine/oemcrypto/mock/src/oemcrypto_session.cpp

@@ -749,10 +749,7 @@ OEMCryptoResult SessionContext::InstallKey(
     return OEMCrypto_ERROR_INVALID_CONTEXT;
   }
   if (!DecryptMessage(content_key, key_control_iv, key_control,
-                      &key_control_str,
-                      (session_keys_->type() == OEMCrypto_EntitlementLicense
-                           ? 256
-                           : 128) /* key size */)) {
+                      &key_control_str, 128 /* key size */)) {
     LOGE("[Installkey(): ERROR: Could not decrypt content key]");
     return OEMCrypto_ERROR_UNKNOWN_FAILURE;
   }