How can I remove an existing lens from the dashboard?

You can remove an existing lens by using the 
removeLens() method and passing the 
key of the lens you want to remove:
\Aero\Admin\Http\Responses\AdminDashboardPage::extend(function (\Aero\Admin\Http\Responses\AdminDashboardPage $page, \Closure $next) {
    $page->removeLens(
        \Aero\Admin\Lenses\OrdersLens::key()
    );
});