Remove unused ReactDOM import

fixes error with mono: "error  'ReactDOM' is defined but never used  no-unused-vars"

(cherry picked from commit 492c9e22bac3c667bc487f2d0ceb18a18fa00655)

frontend/src/Components/FileBrowser/FileBrowserModalContent.js

@@ -1,6 +1,5 @@
 import PropTypes from 'prop-types';
 import React, { Component } from 'react';
-import ReactDOM from 'react-dom';
 import Alert from 'Components/Alert';
 import PathInput from 'Components/Form/PathInput';
 import Button from 'Components/Link/Button';