message: add method to remove connection from ConnectionManager
diff: @@ -27,6 +27,17 @@ public:
  connections.push_back(weak_ptr<ClientContext>(context.shared_from_this()));
  }
  + void RemoveConnection(ClientContext &context) {
  + lock_guard<mutex> lock(connections_lock);
  + for (size_t i = 0; i < connections.size(); i++) {
  + auto connection = connections[i].lock();
  + if (connection == context.shared_from_this()) {
  + connections.erase(connections.begin() + i);
  + return;
  + }
  + }
  + }
  +
  vector<shared_ptr<ClientContext>> GetConnectionList() {
  vector<shared_ptr<ClientContext>> result;
  for (size_t i = 0; i < connections.size(); i++) {
  