Use the new JSX transform (#25064)

app/javascript/mastodon/features/standalone/compose/index.jsx

@@ -1,10 +1,10 @@
-import React from 'react';
+import { PureComponent } from 'react';
 import ComposeFormContainer from '../../compose/containers/compose_form_container';
 import NotificationsContainer from '../../ui/containers/notifications_container';
 import LoadingBarContainer from '../../ui/containers/loading_bar_container';
 import ModalContainer from '../../ui/containers/modal_container';
 
-export default class Compose extends React.PureComponent {
+export default class Compose extends PureComponent {
 
   render () {
     return (