chore(dialog): remove dialog service and all associated

BREAKING CHANGE: The Dialog service will no longer be available

To migrate your code, use the Assistant v1 or v2 service.

Author: dpopp07

README.md

@@ -759,7 +759,6 @@ See [CONTRIBUTING](https://github.com/watson-developer-cloud/node-sdk/blob/maste
 [watson-dashboard]: https://console.bluemix.net/dashboard/apps?category=watson
 [npm_link]: https://www.npmjs.com/package/watson-developer-cloud
 [request_github]: https://github.com/request/request
-[dialog_migration]: https://console.bluemix.net/docs/services/conversation/index.html
 [examples]: https://github.com/watson-developer-cloud/node-sdk/tree/master/examples
 [document_conversion_integration_example]: https://github.com/watson-developer-cloud/node-sdk/tree/master/examples/document_conversion_integration.v1.js
 [conversation_tone_analyzer_example]: https://github.com/watson-developer-cloud/node-sdk/tree/master/examples/conversation_tone_analyzer_integration