testing: Globally define logging via syslog for charon-systemd

We could make the same change for charon (actually setting it for charon
in strongswan.conf.testing would work for charon-systemd too), however,
there are dozens of test cases that currently set charondebug in
ipsec.conf.

testing/tests/tnc/tnccs-20-pdp-eap/hosts/alice/etc/strongswan.conf

@@ -4,9 +4,6 @@ charon-systemd {
   load = random nonce aes sha1 sha2 md5 pem pkcs1 gmp hmac x509 revocation curl vici socket-default kernel-netlink eap-identity eap-ttls eap-md5 eap-tnc tnc-pdp tnc-imv tnc-tnccs tnccs-20 sqlite
 
   syslog {
-    auth {
-      default = 0
-    }
     daemon {
       tnc = 2
       imv = 3