Handle SSL certificate verifications for others than Let's Encrypt

Do no longer (wrongly) rewrite URLs like

  * http://example.net/.well-known/pki-validation/file.txt (Comodo)
  * http://example.net/.well-known/pki-validation/fileauth.txt (DigiCert, Thawte, GeoTrust)
  * http://example.net/.well-known/pki-validation/gsdv.txt (GlobalSign)
  * http://example.net/.well-known/pki-validation/starfield.htm (Starfield, GoDaddy)
  * http://example.net/.well-known/pki-validation/swisssign-check.txt

 (SwissSign)

for automated SSL certificate verifications. All (common commercial)
certificate authorities (CA) except Let's Encrypt (via ACME) seem to
use "pki-validation" rather "acme-challenge" for their domain control
validation (DCV).

Signed-off-by: Robert Scheck <robert@fedoraproject.org>