Revert "FEATURE: Support backup uploads/downloads directly to/from S3."

This reverts commit c29a4dddc1694e2805944f4d5fd0f4fd4514092e.

We're doing a beta bump soon so un-revert this after that is done.

app/assets/javascripts/admin/controllers/admin-backups-index.js.es6

@@ -1,15 +1,9 @@
 import { ajax } from "discourse/lib/ajax";
-import computed from "ember-addons/ember-computed-decorators";
 
 export default Ember.Controller.extend({
   adminBackups: Ember.inject.controller(),
   status: Ember.computed.alias("adminBackups.model"),
 
-  @computed
-  localBackupStorage() {
-    return this.siteSettings.backup_location === "local";
-  },
-
   uploadLabel: function() {
     return I18n.t("admin.backups.upload.label");
   }.property(),