title: Delete entity in google datastore in python
body: <p>I want to delete/modify an entity in the google cloud datastore based on an email.</p>
  
  <pre><code>email = 'john@gmail.com'
  query = client.query('email', '=', email)
  # delete this entity if it exists??
  </code></pre>
  
  <p>Now that I have this query, how can I go about deleting this entity?</p>