Fix hydration race condition (#3240)

* Fix mount_to_root

* Remove WebsysDom.mount

packages/interpreter/src/unified_bindings.rs

@@ -44,9 +44,6 @@ mod js {
     #[extends(BaseInterpreter)]
     pub struct Interpreter;
 
-    fn mount_to_root() {
-        "{this.appendChildren(this.root, this.stack.length-1);}"
-    }
     fn push_root(root: u32) {
         "{this.pushRoot(this.nodes[$root$]);}"
     }