Change FanoutChannel to synchronously process handle destruction.

Summary: This ensures that closing a FanoutChannel will synchronously cancel its input receiver. We don't need to run this code on the provided executor, because it is not running as part of a callback (and because we already have a lock).

Reviewed By: aary

Differential Revision: D32191795

fbshipit-source-id: 9ec2a2303a12580e052de7af8651ebf5b773b8b6

folly/experimental/channels/FanoutChannel-inl.h

@@ -180,10 +180,8 @@ class FanoutChannelProcessor
    * This is called when the user's FanoutChannel object has been destroyed.
    */
   void destroyHandle(CloseResult closeResult) {
-    executor_->add([=, closeResult = std::move(closeResult)]() mutable {
-      auto state = state_.wlock();
-      processHandleDestroyed(state, std::move(closeResult));
-    });
+    auto state = state_.wlock();
+    processHandleDestroyed(state, std::move(closeResult));
   }
 
   /**