eslint: Enable object-shorthand avoidExplicitReturnArrows option.

This is equivalent in the absence of ‘this’ (which ESLint knows to
check for).

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/user_status_ui.js

@@ -40,7 +40,7 @@ export function open_user_status_modal() {
         id: "set_user_status_modal",
         on_click: submit_new_status,
         post_render: user_status_post_render,
-        on_shown: () => {
+        on_shown() {
             input_field().trigger("focus");
         },
     });