title: Delete user meta based on key value that is an array
body: <p>I have a user meta key <code>prize</code> which is an array contains <code>prize type</code> and <code>prize date</code>.
  The date in unix timestamp.
  How I can delete the user meta by specify the prize date only?</p>
  
  <p>Example code:</p>
  
  <pre><code>delete_user_meta( $userID, 'prize', $meta_value ); 
  $meta_value = array(
      'prize' =&gt; array(
           // Add something here like prize date = 1506556467
      ) , 
  );
  </code></pre>
  
  <p>Key value in the database look like this:</p>
  
  <pre><code>a:2:{i:0;s:17:"prize name";i:1;i:1506556467;}
  </code></pre>