Fix more deprecations:

- Remove all `needs:` code

app/assets/javascripts/admin/controllers/modals/admin-badge-preview.js.es6

@@ -1,11 +1,9 @@
 import { escapeExpression } from 'discourse/lib/utilities';
 
 export default Ember.Controller.extend({
-  needs: ['modal'],
-
-  sample: Em.computed.alias('model.sample'),
-  errors: Em.computed.alias('model.errors'),
-  count: Em.computed.alias('model.grant_count'),
+  sample: Ember.computed.alias('model.sample'),
+  errors: Ember.computed.alias('model.errors'),
+  count: Ember.computed.alias('model.grant_count'),
 
   count_warning: function() {
     if (this.get('count') <= 10) {

app/assets/javascripts/admin/controllers/modals/admin-edit-badge-groupings.js.es6

@@ -1,6 +1,5 @@
 import { ajax } from 'discourse/lib/ajax';
 export default Ember.Controller.extend({
-  needs: ['modal'],
 
   modelChanged: function(){
     const model = this.get('model');

app/assets/javascripts/admin/controllers/modals/admin-start-backup.js.es6

@@ -2,31 +2,27 @@ import ModalFunctionality from 'discourse/mixins/modal-functionality';
 import Backup from 'admin/models/backup';
 
 export default Ember.Controller.extend(ModalFunctionality, {
-  needs: ["adminBackupsLogs"],
+  adminBackupsLogs: Ember.inject.controller(),
 
-  _startBackup: function (withUploads) {
-    var self = this;
-    Discourse.User.currentProp("hideReadOnlyAlert", true);
-    Backup.start(withUploads).then(function() {
-      self.get("controllers.adminBackupsLogs").clear();
-      self.send("backupStarted");
+  _startBackup(withUploads) {
+    this.currentUser.set('hideReadOnlyAlert', true);
+    Backup.start(withUploads).then(() => {
+      this.get("adminBackupsLogs.logs").clear();
+      this.send("backupStarted");
     });
   },
 
   actions: {
-
-    startBackup: function () {
+    startBackup() {
       this._startBackup();
     },
 
-    startBackupWithoutUpload: function () {
+    startBackupWithoutUpload() {
       this._startBackup(false);
     },
 
-    cancel: function () {
+    cancel() {
       this.send("closeModal");
     }
-
   }
-
 });