Correct CancelKeyRequest behavior

[ Merge of https://widevine-internal-review.googlesource.com/#/c/10659/
  from the widevine cdm repo. ]

CdmEngine::CancelKeyRequest would earlier release keys by closing and
reopening a crypto session. Behavior has been changed to just close
the session.

b/15984869

Change-Id: I92a1f82fd4a97b5510596d4bc69bf07406cee606

libwvdrmengine/cdm/core/src/cdm_engine.cpp

@@ -299,8 +299,7 @@ CdmResponseType CdmEngine::CancelKeyRequest(const CdmSessionId& session_id) {
     return KEY_ERROR;
   }
 
-  // Re-initialize to release crypto session/keys without closing session
-  iter->second->Init();
+  iter->second->CancelKeyRequest();
   return NO_ERROR;
 }