Plugin/Magento/Customer/Model/ResourceModel/CustomerRepository.php
public function beforeDeleteById(
        \Magento\Customer\Api\CustomerRepositoryInterface $subject,
        $customerId
    ) {
        $this->deleteDwnl($customerId);
        $result = [$customerId];
        return $result;
    }
public function beforeDeleteById(
        \Magento\Customer\Api\CustomerRepositoryInterface $subject,
        $customerId
    ) {
        $this->deleteDwnl($customerId);
        $result = [$customerId];
        return $result;
    }
Remove customer related data from Bonus Hybrid tables on customer delete from adminhtml.

@param \Magento\Customer\Api\CustomerRepositoryInterface $subject
@param $customerId
@return array