kamailio.cfg: removed sample db_mode parameter for domain module

- no longer exists since 3.3 domain update

etc/kamailio.cfg

@@ -380,8 +380,6 @@ modparam("speeddial", "use_domain", MULTIDOMAIN)
 # ----- domain params -----
 #!ifdef WITH_MULTIDOMAIN
 modparam("domain", "db_url", DBURL)
-# use caching
-modparam("domain", "db_mode", 1)
 # register callback to match myself condition with domains list
 modparam("domain", "register_myself", 1)
 #!endif