Add dropdown for boost privacy in boost confirmation modal (#15704)

* Various dropdown code quality fixes

* Prepare support for privacy selection in boost modal

* Add dropdown for boost privacy in boost confirmation modal

app/javascript/mastodon/features/compose/containers/privacy_dropdown_container.js

@@ -5,7 +5,6 @@ import { openModal, closeModal } from '../../../actions/modal';
 import { isUserTouching } from '../../../is_mobile';
 
 const mapStateToProps = state => ({
-  isModalOpen: state.get('modal').modalType === 'ACTIONS',
   value: state.getIn(['compose', 'privacy']),
 });