how to use hook deleted_user into custom function to delete user from custom table

Using the delete_user action you can pass in the user_id and use that as a basis to delete the user from your addtiional table. This is, of course, assuming you use the user_id to make a relation between the two table. If not you can use get_userdata() passing in the user_id to get more user information. It would look something like this:

function custom_remove_user( $user_id ) {
    // $user_meta = get_userdata( $user_id );    // IF you need additional user info before removal
    ...
}
add_action( 'delete_user', 'custom_remove_user', 10 );