code: @Synchronized
      public <T extends Notification> void removeListener(final String type, final Listener<T> listener) {
          map.get(type).removeIf(e -> e.getListener().equals(listener));
      }
docs: Remove Listener of a given notification type.
  
  @param <T>      Type of notification.
  @param type     Type of notification listener.
  @param listener Listener to be removed.