code: public static String removeExtensionProvider(String elementName, String namespace) {
          String key = getKey(elementName, namespace);
          extensionProviders.remove(key);
          return key;
      }
docs: Removes an extension provider with the specified element name and namespace. This
  method is typically called to cleanup providers that are programmatically added
  using the {@link #addExtensionProvider(String, String, Object) addExtensionProvider} method.
  
  @param elementName the XML element name.
  @param namespace the XML namespace.
  @return the key of the removed stanza extension provider