Remove unnecessary and incorrect find('.menu').toggle() (#22987)

Follows:
* #22950

The dropdown menu works well without these codes.

The reason is that the event bubbling still works for the dropdown menu,
the Fomantic UI dropdown menu module will hide the menu correctly if an
item is clicked.

web_src/js/features/repo-issue.js

@@ -552,8 +552,6 @@ export function initRepoIssueReferenceIssue() {
   // Reference issue
   $(document).on('click', '.reference-issue', function (event) {
     const $this = $(this);
-    $this.closest('.dropdown').find('.menu').toggle('visible');  // eslint-disable-line
-
     const content = $(`#${$this.data('target')}`).text();
     const poster = $this.data('poster-username');
     const reference = $this.data('reference');