Perch does not ship with these files as Clive Walker mentioned.
I'm not sure what they mean by "response headers".
You can check the response header with your browser's DevTools. You can learn more about them: https://developer.mozilla.org/…/Glossary/Response_header
X-Powered-By is a common non-standard HTTP header that some servers send along with their response headers. The header often provides information on the type server and in your case the version of PHP installed. Disable this header (and review the other headers the server sends) or ask your web host to do so.