Hi,
That's the code which checks that the payment notifications come from a PayPal server by sending a request to PayPal servers.
That means that we can't guarantee that the payment notifications will come from PayPal and it could be a forgery.
There is still a check on the IP address from the sender of the notification, but it's possible (not easy) to falsify it and that why we had also that request to PayPal servers.
If you want to get the code from that file, just download again the installation package from our website and extract it. The file will be in the folder back/extensions/plg_hikashoppayment_paypal/ of the package.