certs: remove caas backend

src/test/apptask-test.js

@@ -59,7 +59,7 @@ const DOMAIN_0 = {
         endpoint: 'http://localhost:5353'
     },
     fallbackCertificate: null,
-    tlsConfig: { provider: 'caas' }
+    tlsConfig: { provider: 'letsencrypt-staging' }
 };
 
 let AUDIT_SOURCE = { ip: '1.2.3.4' };