code: public function clearOutgoingContext($contextName)
      {
          foreach ($this->outgoingContexts as $i => $context) {
              if ($context->getName() == $contextName) {
                  unset($this->outgoingContexts[$i]);
              }
          }
  
          return $this;
      }
docs: Clear an existing outgoing context.
  Reference: https://dialogflow.com/docs/contexts.
  
  @param string $contextName
  
  @return \Dialogflow\WebhookClient