Well, it is only usually the admin of the server that needs to set up the database (usually on the install). So you can just tell them in the installation instructions to delete the file once they've setup the server.

Or you can do a test with index.php or some other file that first loads after they've setup the sever like so:

 Code:
<?php
$filename = "db_update.php";

if (file_exists($filename)) {
     echo "Please remove db_update.php";
} else {
// The rest of your code goes here.
}
?>