b=957468 don't unset mNonRealtimeProcessing after offline graph completion r=roc

--HG--
extra : transplant_source : %D1%17%20%079%82%2B%91ES%B5%CC%83%E3t%8B%F9%A8%D6%E7

content/media/MediaStreamGraph.cpp

@@ -1619,11 +1619,6 @@ MediaStreamGraphImpl::AppendMessage(ControlMessage* aMessage)
         gGraph = nullptr;
       }
       delete this;
-    } else if (!mRealtime) {
-      // Make sure to mark the graph as not doing non-realtime processing,
-      // because otherwise AppendMessage will try to ensure that the graph
-      // is running, and we will never manage to release our resources.
-      mNonRealtimeProcessing = false;
     }
     return;
   }