code: public static boolean unregister(Object registryKey) {
          if (registryKey == null) {
              throw new IllegalArgumentException("registryKey must not be null");
          }
  
          if (shim == null) {
              return false;
          }
  
          return shim.unregister(registryKey);
      }
docs: <strong>[icu]</strong> Unregisters the factory or instance associated with this key (obtained from
  registerInstance or registerFactory).
  @param registryKey a key obtained from registerFactory
  @return true if the object was successfully unregistered
  @hide unsupported on Android