Delete settings related to domain on domain deleting
Delete settings related to domain on domain deleting

Because this bug domain deleting isn't possible when 
a domain specific attribute is set (eg. dyndns).

This modification delete domain settings before domain
deleting.
0x97/PowerDNS-Admin,0x97/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,0x97/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,0x97/PowerDNS-Admin