Domain Names cannot be removed/deleted. Once a Domain is registered it remains active until it's expiration date. Once the expiration date is reached, the domain is deleted some time later after the Grace/Redemption period is ended. Because of that, Domain Name registrations are also not refundable.
If you no longer wish to use your Domain Name registration, just let it expire.
NOTE: To completely remove Hostinger profile send an email to firstname.lastname@example.org.