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-hcd-eap/hosts/moon/etc/strongswan.conf

@@ -4,14 +4,6 @@ charon-systemd {
   load = random nonce aes sha1 sha2 md5 pem pkcs1 gmp hmac x509 revocation curl vici kernel-netlink socket-default eap-identity eap-radius updown
   multiple_authentication=no
 
-  syslog {
-    daemon {
-      default = 1
-    }
-    auth {
-      default = 0
-    }
-  }
   plugins {
     eap-radius {
       secret = gv6URkSs