title: Python remove keys with the same value on a dictionary
body: <p>I need to do a not "natural" operation on a dictionary so i wondering what is the best pythonic way to do this.</p>
  
  <p>I need to simplify a dictionary by removing all the keys on it with the same value (keys are differents, values are the same)</p>
  
  <p>For example:
  Input:     </p>
  
  <pre><code>  dict = {key1 : [1,2,3], key2: [1,2,6], key3: [1,2,3]}
  </code></pre>
  
  <p>expected output:</p>
  
  <pre><code>  {key1 : [1,2,3], key2:[1,2,6]}
  </code></pre>
  
  <p>I dont care about which key is delete (on the example: key1 or key3)</p>