[Rspamd] Respect Redis REPLICA in reputation plugin (#4046)

data/conf/rspamd/local.d/reputation.conf

@@ -2,9 +2,7 @@ rules {
   ip_reputation = {
     selector "ip" {
     }
-    backend "redis" {
-      servers = "redis";
-    }
+    backend "redis";
     symbol = "IP_REPUTATION";
   }
 }