Why does WordPress have a noop.php file?

The description on top of the page you have linked gives an explanation:

Create a new file, wp-admin/includes/noop.php, which loads all of the noop functions for load-script|styles.php and is only loaded by those files. DRYs in the process. See #33813.

Additionally there is the trac ticket #33813 linked, which gives some additional insight. You generally shouldn’t delete core files so consider noop.php as a necessary file.