title: Remove duplicated entities from conversation response
body: <p>I had the following <code>@fields</code> entity:</p>
  
  <p><code>innovation</code> => <code>change management</code> (as Synonyms)</p>
  
  <p>When I typed the following in the dialog, </p>
  
  <pre><code>show me innovation and change management fields
  </code></pre>
  
  <p>I got the duplicated entities as:</p>
  
  <pre><code>{
    "intents": [
      {
        "intent": "do.something",
        "confidence": 0.9974480628967286
      }
    ],
    "entities": [
      {
        "entity": "fields",
        "location": [
          23,
          40
        ],
        "value": "innovation",
        "confidence": 1
      },
      {
        "entity": "fields",
        "location": [
          8,
          18
        ],
        "value": "innovation",
        "confidence": 1
      }
    ]
  }
  </code></pre>
  
  <p>I'm expecting to get ONLY one, as I had ONLY one entity with <code>innovation</code> or <code>change management</code> values. I'm sure no other entities has these two keywords.</p>
  
  <p>Is that a bug! or it's normal behaviour!</p>