ui: Also remove the places we were using the files, like the tests

We also referred to confirm/error in the confirmation dialog, but they
were never used (ever since we moved from native dialogs to HTML ones).

We lef tthe ability to use native dialogs, but we are never going to go
back there so we may as well remove them now.

ui-v2/app/components/confirmation-dialog.js

@@ -3,7 +3,6 @@ import Component from '@ember/component';
 
 import SlotsMixin from 'block-slots';
 import { set } from '@ember/object';
-import { inject as service } from '@ember/service';
 
 const cancel = function() {
   set(this, 'confirming', false);
@@ -15,25 +14,10 @@ const confirm = function() {
   const [action, ...args] = arguments;
   set(this, 'actionName', action);
   set(this, 'arguments', args);
-  if (this._isRegistered('dialog')) {
-    set(this, 'confirming', true);
-  } else {
-    this._confirm
-      .execute(this.message)
-      .then(confirmed => {
-        if (confirmed) {
-          this.execute();
-        }
-      })
-      .catch(function() {
-        return this.error.execute(...arguments);
-      });
-  }
+  set(this, 'confirming', true);
 };
 export default Component.extend(SlotsMixin, {
   classNameBindings: ['confirming'],
-  _confirm: service('confirm'),
-  error: service('error'),
   classNames: ['with-confirmation'],
   message: 'Are you sure?',
   confirming: false,