title: "Imagick::flattenImages method is deprecated and it's use should be avoided"
body: <p>i cant use flatternImages() function becouse it's deprecated.</p>
  
  <p>I must use</p>
  
  <pre><code>$im-&gt;setImageAlphaChannel(\Imagick::ALPHACHANNEL_REMOVE);
  $im-&gt;mergeImageLayers(\Imagick::LAYERMETHOD_FLATTEN);
  </code></pre>
  
  <p>But ALPHACHANNEL_REMOVE constant is undefined.</p>
  
  <p>How can i solve this issue?</p>
  
  <p>P.S.
  I tried to use 11 instead \Imagick::ALPHACHANNEL_REMOVE and get error:</p>
  
  <blockquote>
    <p>"Unable to set image alpha channel"</p>
  </blockquote>