How to disable admin flyout menus?

Seriously, I hate flyout menus with a passion, and now they’re popping up all over the place in the admin screen. (They are particularly heinous when you use the blue admin theme, because they add a dark arrow. Eye dirt.)

How do I disable the flyout menu? They add zero functionality and usability to my workflow.

Thanks

It’s a bit of a workarround but here you go:

function remove_flyout() {
   echo '<style type="text/css">
        .js #adminmenu .wp-submenu.sub-open {
            display: none;
        }
    </style>';
}
add_action('admin_head', 'remove_flyout');

Put it in your functions.php