message: Remove the now unneeded last_updater.
diff: @@ -137,13 +137,7 @@ public:
  *
  * @return the updater object
  */
  - Updater &update()
  - {
  - last_updater.reset(new Updater{this});
  - return *(last_updater.get());
  - }
  -
  - const Updater &get_updater() const { return *last_updater.get(); }
  + Updater update() { return {this}; }
  /**
  * This checks whether convergence was reached for a certain criterion.
  @@ -178,12 +172,7 @@ protected:
  explicit Criterion(std::shared_ptr<const gko::Executor> exec)
  : EnableAbstractPolymorphicObject<Criterion>(exec)
  - {
  - this->last_updater = std::unique_ptr<Updater>(new Updater{this});
  - }
  -
  -private:
  - std::unique_ptr<Updater> last_updater;
  + {}
  };
  