Record's TTL is required to delete a RecordSet

If the previous record set has a non-default TTL set, the Route53 API
will refuse to honor the DELETE request if the TTL isn't included in the
change. This change uses the exact values from the ResourceRecordSet
that is being replaced.
Merge pull request #229 from HealthUnlocked/fix-cname-delete

Record's TTL is required to delete a RecordSet