Add unit test for preloaded license

Merge from Widevine repo of http://go/wvgerrit/96508

This adds a unit test for to verify that a preloaded license may be
loaded into OEMCrypto. A preloaded license is a license that does not
have a nonce, and for which there is no license request. This is used
in CAS and ATSC.

I also updated the test version string to
OEMCrypto unit tests for API 16.2. Tests last updated 2020-03-27

Bug: 144105097
Test: ran oemcrypto unit tests on taimen and with v16 modmock.
Change-Id: I6a4926917f36a084d15defa7b908d067612c4dcf

libwvdrmengine/oemcrypto/test/oec_session_util.cpp

@@ -586,9 +586,6 @@ void LicenseRoundTrip::EncryptAndSignResponse() {
   memcpy(encrypted_response_.data() + serialized_core_message_.size(),
          reinterpret_cast<const uint8_t*>(&encrypted_response_data_),
          sizeof(encrypted_response_data_));
-  if (global_features.provisioning_method == OEMCrypto_OEMCertificate) {
-    session()->GenerateDerivedKeysFromSessionKey();
-  }
   session()->key_deriver().ServerSignBuffer(encrypted_response_.data(),
                                             encrypted_response_.size(),
                                             &response_signature_);