Revert "Use some for needsRebuild in SubtreeRetainer"

This reverts commit 5318bd456856407dd92f44583bed5c88f0813a80.

My bad, I did not realize there was a side effect (storing stuff in
this.data) when suggesting this change. With that, using some() is much
less useful - plus it probably causes a bug because it does not always
iterate over all items once the callback returns true.

js/src/common/utils/SubtreeRetainer.js

@@ -33,16 +33,18 @@ export default class SubtreeRetainer {
    * @public
    */
   needsRebuild() {
-    return this.callbacks.some((callback, i) => {
+    let needsRebuild = false;
+
+    this.callbacks.forEach((callback, i) => {
       const result = callback();
 
       if (result !== this.data[i]) {
         this.data[i] = result;
-        return true;
+        needsRebuild = true;
       }
-
-      return false;
     });
+
+    return needsRebuild;
   }
 
   /**