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/clipboard.js

@@ -1,3 +1,5 @@
+import $ from 'jquery';
+
 const {copy_success, copy_error} = window.config.i18n;
 
 function onSuccess(btn) {