code: public function remove($identifier, $shardingKey)
      {
          $sources = array();
          foreach ($this->configuration['properties'] as $properties) {
              if (isset($properties['sources'])) {
                  foreach ($properties['sources'] as $sourceName) {
                      if (false === isset($sources[$sourceName])) {
                          $sources[$sourceName] = $this->sourceManager->getSource($sourceName);
                      }
                  }
              }
          }
          foreach ($this->configuration['sources'] as $sourceName) {
              if (false === isset($sources[$sourceName])) {
                  $sources[$sourceName] = $this->sourceManager->getSource($sourceName);
              }
          }
  
          $mappedIdentifiers = array();
          foreach ($identifier as $id => $value) {
              $mappedIdentifiers[$this->getFieldNameFromProperty($id)] = $value;
          }
  
          foreach ($sources as $source) {
              $source->remove($mappedIdentifiers, $shardingKey);
          }
  
          return $this;
      }
docs: @param mixed $identifier
  @param mixed $shardingKey
  
  @return $this