FIX: Remove custom 'error' action on build-category-route/discovery (#11425)

The root cause of the issue was that the route was overriding the 'error' action from the correctly implemented handler in routes/application.js.

Remove the custom handler, and the duplicated template logic for displaying the errorHtml.

Fixes: e16b3da04a

app/assets/javascripts/discourse/app/routes/build-category-route.js

@@ -66,16 +66,11 @@ export default (filterArg, params) => {
           parts.pop();
         }
 
-        return Category.reloadBySlugPath(parts.join("/"))
+        return Category.reloadBySlugPath(parts.join("/")).then((result) => {
-          .then((result) => {
           const record = this.store.createRecord("category", result.category);
           record.setupGroupsAndPermissions();
           this.site.updateCategory(record);
           return { category: record, modelParams };
-          })
-          .catch(() => {
-            // afterModel will call replaceWith(/404)
-            return null;
         });
       }
 
@@ -244,18 +239,6 @@ export default (filterArg, params) => {
     },
 
     actions: {
-      error(err) {
-        const json = err.jqXHR.responseJSON;
-        if (json && json.extras && json.extras.html) {
-          this.controllerFor("discovery").set(
-            "errorHtml",
-            err.jqXHR.responseJSON.extras.html
-          );
-        } else {
-          this.replaceWith("exception");
-        }
-      },
-
       setNotification(notification_level) {
         this.currentModel.setNotification(notification_level);
       },

app/assets/javascripts/discourse/app/templates/discovery.hbs

@@ -1,6 +1,3 @@
-{{#if errorHtml}}
-  {{html-safe errorHtml}}
-{{else}}
 <div class="container">
   {{discourse-banner user=currentUser banner=site.banner}}
   {{#unless viewingCategoriesList}}
@@ -38,4 +35,3 @@
 </div>
 
 {{plugin-outlet name="discovery-below"}}
-{{/if}}