Remove unused variables (#3906)

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

@@ -1,7 +1,7 @@
 import { connect } from 'react-redux';
 import UploadProgress from '../components/upload_progress';
 
-const mapStateToProps = (state, props) => ({
+const mapStateToProps = state => ({
   active: state.getIn(['compose', 'is_uploading']),
   progress: state.getIn(['compose', 'progress']),
 });