[DOC] remove buggy comment for use_backend

"early blocking based on ACLs" is definitely wrong here
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 5d70341..416e67c 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -1273,7 +1273,7 @@
 		LIST_INIT(&rule->list);
 		LIST_ADDQ(&curproxy->redirect_rules, &rule->list);
 	}
-	else if (!strcmp(args[0], "use_backend")) {  /* early blocking based on ACLs */
+	else if (!strcmp(args[0], "use_backend")) {
 		int pol = ACL_COND_NONE;
 		struct acl_cond *cond;
 		struct switching_rule *rule;