CLEANUP: proto_http: remove useless initialisation

This initialisation of the opaque array is useless.
diff --git a/src/proto_http.c b/src/proto_http.c
index 4cb9483..d5b2c69 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -12618,7 +12618,6 @@
 	}
 	cur_arg++;
 
-	LIST_INIT((struct list *)&rule->arg.act.p[0]);
 	proxy->conf.args.ctx = ARGC_CAP;
 
 	rule->action       = HTTP_RES_ACT_CUSTOM_CONT;