Use explicit jQuery import, remove unused eslint globals (#18435)

- Don't rely on globals (window.$) for jQuery import
- Remove eslint globals no longer in use

web_src/js/features/repo-editor.js

@@ -1,9 +1,9 @@
+import $ from 'jquery';
 import {htmlEscape} from 'escape-goat';
 import {initMarkupContent} from '../markup/content.js';
 import {createCodeEditor} from './codeeditor.js';
 
 const {csrfToken} = window.config;
-
 let previewFileModes;
 
 function initEditPreviewTab($form) {