Clean up fuzz helper classes

- Remove OEMCrypto state changes hidden in constructors and destructors.
- Use composition instead of inheritance to structure classes.
- Avoid calling non-trivial destructors for objects with static
  lifetime.

Merged from https://widevine-internal-review.googlesource.com/168497
Merged from https://widevine-internal-review.googlesource.com/171170
Merged from https://widevine-internal-review.googlesource.com/171171
Merged from https://widevine-internal-review.googlesource.com/171870

Change-Id: I20476a7b1132d11f011b8650ec01e3c2dc3fc0e8

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_opk_dispatcher_fuzz.cc

@@ -3,7 +3,7 @@
 #include "opk_dispatcher.h"
 #include "opk_init.h"
 
-namespace wvoec {
+namespace {
 
 void OpenOEMCryptoTASession() {
   uint8_t request_body[] = {
@@ -35,6 +35,8 @@ void InitializeOEMCryptoTA() {
   OPK_DispatchMessage(&request, &response);
 }
 
+} // namespace
+
 extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv) {
   OPK_Initialize();
   InitializeOEMCryptoTA();
@@ -51,5 +53,3 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   OPK_DispatchMessage(&request, &response);
   return 0;
 }
-
-}  // namespace wvoec