Hide all admin notices and notifications

function wpcb_hide_admin_notices() {

    ?>

    <style>

        .notice,

        .notice-error, 

        .notice-warning, 

        .notice-success, 

        .notice-info, 

        .error,

        .update-nag {

            display: none !important;

        }

    </style>

    <?php

}

add_action('admin_head', 'wpcb_hide_admin_notices', 5 );