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/swanctl/net2net-multicast/hosts/moon/etc/strongswan.conf

@@ -9,14 +9,6 @@ charon-systemd {
 
   multiple_authentication = no
 
-  syslog {
-    daemon {
-      default = 1
-    }
-    auth {
-      default = 0
-    }
-  }
   plugins {
     forecast {
       groups = 224.0.0.251

testing/tests/swanctl/net2net-multicast/hosts/sun/etc/strongswan.conf

@@ -5,14 +5,6 @@ charon-systemd {
 
   multiple_authentication = no
 
-  syslog {
-    daemon {
-      default = 1
-    }
-    auth {
-      default = 0
-    }
-  }
   plugins {
     forecast {
       groups = 224.0.0.251