Revert "model.js restore open cluster on merge"

This reverts commit 75e01801.

browser/js/model.js

@@ -1159,7 +1159,6 @@ Model.prototype = {
             this.clusters[list[i]] = [];
         }
 
-        this.clone(leader).split = true;
         this.clusters[leader] = new_cluster;
         this.unselectAll()
         this.updateElem(list)