title: PropType is defined but prop is never used for arrow function with single argument
body: <p>Say i have code like this</p>
  
  <pre><code>const MessageBody = inner =&gt; (
    // eslint-disable-next-line react/no-danger
    &lt;div dangerouslySetInnerHTML={{ __html: inner }} /&gt;
  );
  
  MessageBody.propTypes = {
    /**
     * Message itself, this can be a html element or plain string
     */
    inner: PropTypes.oneOfType([
      PropTypes.string,
      PropTypes.element,
    ]),
  };
  </code></pre>
  
  <p>Eslint says 
  'inner' PropType is defined but prop is never used lint(react/no-unused-prop-types)</p>
  
  <p>How to fix this please ?</p>