settings: only import required action

Fixes crash on mobile due to chained imports.

react/features/settings/actions.js

 import { openDialog } from '../base/dialog';
 import { i18next } from '../base/i18n';
 import { updateSettings } from '../base/settings';
-import { setPrejoinPageVisibility } from '../prejoin';
+import { setPrejoinPageVisibility } from '../prejoin/actions';
 
 import {
     SET_AUDIO_SETTINGS_VISIBILITY,