tests: Remove unused .css = noop.

The front end tests pass without these removed lines. There are a few
such lines that are still necessary.

web/tests/popover_menus_data.test.cjs

@@ -153,8 +153,6 @@ function set_page_params_no_edit_restrictions({override}) {
 function test(label, f) {
     run_test(label, (helpers) => {
         // Stubs for calculate_timestamp_widths()
-        $("<div>").css = noop;
-        $(":root").css = noop;
         $("<div>").width = noop;
         $("<div>").remove = noop;