Fix bugs impacting fuzzing coverage

- Update ConvertDataToValidEnum to not use FuzzedDataProvider since it
  causes unexpected parsing results.
- Add OEMCryptoLicenseAPIFuzz::LoadLicenseWithGenericCryptoKeys so that
  generic crypto fuzz tests can load appropriate keys.
- Remove custom mutator from oemcrypto_generic_verify_fuzz because it
  provides minimal additional coverage.
- Refresh affected corpus files.

Merged from https://widevine-internal-review.googlesource.com/168557
Merged from https://widevine-internal-review.googlesource.com/171191
Merged from https://widevine-internal-review.googlesource.com/172170
Merged from https://widevine-internal-review.googlesource.com/172250

Change-Id: Ie676a36cbf4c12bdda9566fad3590a7b69168d9c

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_generic_sign_fuzz.cc

@@ -20,7 +20,7 @@ wvoec::OEMCryptoLicenseAPIFuzz& license_api_fuzz =
 extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv) {
   wvoec::RedirectStdoutToFile();
   license_api_fuzz.Initialize();
-  license_api_fuzz.LoadLicense();
+  license_api_fuzz.LoadLicenseWithGenericCryptoKeys();
   return 0;
 }
 
@@ -33,18 +33,19 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   FuzzedDataProvider fuzzed_data(data, size);
   fuzzed_data.ConsumeData(&fuzzed_structure, sizeof(fuzzed_structure));
   wvoec::ConvertDataToValidEnum(OEMCrypto_CipherMode_MaxValue,
-                                &fuzzed_structure.cipher_mode);
+                                fuzzed_structure.cipher_mode);
   wvoec::ConvertDataToValidEnum(OEMCrypto_Algorithm_MaxValue,
-                                &fuzzed_structure.algorithm);
+                                fuzzed_structure.algorithm);
   // Copy clear buffer from input data.
   const std::vector<uint8_t> clear_buffer =
       fuzzed_data.ConsumeRemainingBytes<uint8_t>();
 
+  // Select key and sign.
   wvoec::Session& session = license_api_fuzz.session();
   std::vector<uint8_t> key_handle;
   wvoec::GetKeyHandleIntoVector(session.session_id(),
-                                session.license().keys[0].key_id,
-                                session.license().keys[0].key_id_length,
+                                session.license().keys[2].key_id,
+                                session.license().keys[2].key_id_length,
                                 fuzzed_structure.cipher_mode, key_handle);
   size_t signature_length = 0;
   OEMCrypto_Generic_Sign(key_handle.data(), key_handle.size(),