While you can delete individual themes and copies of themes in the theme tab, the storefront host itself cannot not directly deleted. In lieu of deleting the storefront host, you can "Lock" the storefront host. A locked storefront host is not publicly browsable unless you share the access password with the person browsing there.
Please Note:
Locking a storefront removes the storefront host from your storefront count, so it effectively "deletes" it from affecting your service plan due to storefront host count.
Related Documentation