In order to help guide users to properly install the plugin when it has been cloned from GitHub, the plugin includes this code:

As potentially discovered on the support forum, the file_exists() check may return stale results that necessitate calling clearstatcache().

Nevertheless, this entire if statement is irrelevant from being included in plugin builds distributed from WordPress.org because we already know that those files exist at build time. So we can potentially prevent a bug from happening and improve performance a tiiiiiiny bit by just removing it entirely from amp.php during a build.