code: public boolean removeReference(ServiceReference<T> reference) {
          synchronized (elementMap) {
              ConcurrentServiceReferenceElement<T> element = elementMap.remove(reference);
              if (element == null) {
                  return false;
              }
  
              elementSet.remove(element);
              return true;
          }
      }
docs: Removes the service reference from the set
  
  @param reference ServiceReference associated with service to be unset
  @return true if this set contained the service reference