Why would you do that? But even more to the point, how would you do that? The instructions call for your Cloudflare API key. If you don’t have a Cloudflare account, you don’t have a Cloudflare API key. So what did you enter as your API key?
In any event, the following should correct your problem and return you to a self-signed certificate:
config delprop pki CrtFile
config delprop pki KeyFile
config delprop pki ChainFile
signal-event nethserver-base-update
Once you’ve done that, confirm that the key file is again present:
ls -l /etc/pki/tls/private