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-branch.js

@@ -1,3 +1,5 @@
+import $ from 'jquery';
+
 export function initRepoBranchButton() {
   $('.show-create-branch-modal.button').on('click', function () {
     $('#create-branch-form')[0].action = $('#create-branch-form').data('base-action') + $(this).data('branch-from-urlcomponent');