testing: Configure logging via syslog in strongswan.conf

Globally configure logging in strongswan.conf.testing and replace all
charondebug statements with strongswan.conf settings.

testing/hosts/default/etc/strongswan.conf.testing

@@ -7,8 +7,6 @@ charon {
       xfrm_acq_expires = 60
     }
   }
-}
-charon-systemd {
   syslog {
     daemon {
     }