Address NTS TCs AUDIO-026-* failures

[ Merge of http://go/wvgerrit/66083 and http://go/ag/5445191 ]

Fix proposed by amlogic. Release usage session early in the CdmEngine
destructor to avoid SIGBUS.

Bug: 118646062
Test: WV unit/integration tests.

Change-Id: I8b419c57814dc32e9873173ab6c24d209bdcc3a0

libwvdrmengine/cdm/core/src/cdm_engine.cpp

@@ -86,6 +86,7 @@ CdmEngine::CdmEngine(FileSystem* file_system, const std::string& spoid)
 }
 
 CdmEngine::~CdmEngine() {
+  usage_session_.reset();
   AutoLock lock(session_map_lock_);
   session_map_.Terminate();
 }