title: How do I prohibit a specific function call with Rubocop?
body: <p>I have a Rails project where we're migrating towards using an image proxy to serve our ActiveStorage images. As part of this migration, we need to change all existing usages of <code>url_for()</code> to <code>ix_image_url()</code>.</p>
  <p><code>url_for</code> will continue to exist, but in order to prevent other developers from accidentally using the wrong function in the future and accidentally serving an unproxied image, I'd like to &quot;ban&quot; use of <code>url_for</code> within our project.</p>
  <p>Is this possible?</p>