code: public boolean removeSubscribeListener(SubscribeListener subscribeListener) {
          boolean removed = subscribeListeners.remove(subscribeListener);
          if (removed && subscribeListeners.isEmpty()) {
              setSubscriptionMode(previousSubscriptionMode);
          }
          return removed;
      }
docs: Remove a subscribe listener. Also restores the previous subscription mode
  state, if the last listener got removed.
  
  @param subscribeListener
  the subscribe listener to remove.
  @return <code>true</code> if the listener registered and got removed.
  @since 4.2