mepr-remove-unauthorized-meta-box.php

<?php

function mepr_remove_unauthorized_meta_box() {
    if ( ! current_user_can( 'administrator' ) ) {
        foreach ( get_post_types() as $post_type ) {
            remove_meta_box( 'mepr_unauthorized_message', $post_type, 'advanced' );
        }
    }
}
add_action( 'admin_head', 'mepr_remove_unauthorized_meta_box' );