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-diff.js

@@ -1,6 +1,8 @@
+import $ from 'jquery';
 import {initCompReactionSelector} from './comp/ReactionSelector.js';
 import {initRepoIssueContentHistory} from './repo-issue-content.js';
 import {validateTextareaNonEmpty} from './comp/EasyMDE.js';
+
 const {csrfToken} = window.config;
 
 export function initRepoDiffReviewButton() {