Disable unused 'tls' clause options: 'ca-file' and 'hostname'

This commit disables the unused 'tls' clause options. For these some
backing code exists, but their values are not really used anywhere,
nor there are sufficient syntax tests for them.

These options are only disabled temporarily, until TLS certificate
verification gets implemented.

bin/tests/system/checkconf/good-dot-doh-tls-nokeycert.conf

@@ -12,5 +12,4 @@
 # In some cases a "tls" statement may omit key-file and cert-file.
 tls local-tls {
     protocols {TLSv1.2;};
-    hostname "fqdn.example.com";
 };