MC-5691: Implement better developer error reporting

- Remove legacy function
- Re-generate ts-errors.json

Author: davemacaulay

app/code/Magento/PageBuilder/view/adminhtml/web/js/content-type/preview.js

@@ -575,21 +575,6 @@ export default class Preview {
         return hasDataChanges;
     }
 
-    /**
-     * Retrieve the preview template
-     *
-     * @returns {string}
-     */
-    private getPreviewTemplate() {
-        const appearance = this.parent.dataStore.get("appearance") ?
-            this.parent.dataStore.get("appearance").toString() : undefined;
-
-        return appearanceConfig(
-            this.config.name,
-            appearance,
-        ).preview_template;
-    }
-
     /**
      * Any hidden element should block drag / drop events from uploading images from the OS. We have to block this for
      * all elements as underlying elements could still receive the events if a parent is hidden.