[Rspamd] Remove explict redis servers from statistic, add a name

data/conf/rspamd/local.d/statistic.conf

@@ -4,7 +4,7 @@ classifier "bayes" {
     }
 
     backend = "redis";
-    servers = "redis:6379";
+    name = "per_domain_bayes";
     min_tokens = 11;
     min_learns = 20;
     autolearn = [-20, 50];