[vvoytovych]

A record set that changes type keeps its old record in PowerDNS. When an ALIAS becomes a CNAME, the old ALIAS blocks the new CNAME, and the record set reports a conflict with itself. Deleting the record set leaves the old record behind.

This removes every record a record set wrote and no longer wants, whatever its type.

Change	Effect
Update and delete remove the record set's own records of every type, not only of its current type	a record set that changes type publishes with no manual step, and a deleted record set leaves nothing behind
The old record's delete travels in the same request as the new record, ahead of it	if PowerDNS refuses the new record, nothing changes and the old record keeps serving
A conflict message names only records that the record set did not write	the message points at the record that blocks
The agent logs and counts each record of another type that it deletes	a rollout shows what it removed

• Records that another record set wrote, and records that nothing wrote, stay untouched.
• A record set that is already programmed does not reach PowerDNS again until its generation changes, and a resync does not reach it either, so its old records of another type go on its next change or delete. A record set that is not programmed, such as one in conflict with its own old record, reconciles at once on upgrade. A controller comment said a resync corrects drift; it now says that it does not.
• The issue says production is not affected. One production record set is: a test wildcard in our own project conflicts with its own old ALIAS. It clears with this release.
• Use CNAME routing records for non-apex hostnames network-services-operator#564 would convert non-apex ALIAS records to CNAME and meet this on each one.

Test plan

• Locally, on PowerDNS 5.1.4 with LMDB: ALIAS to CNAME and back at one name, each in one request, and a second reconcile sends nothing
• Locally: other record sets' records and unowned records survive a type change and a delete, the apex keeps its SOA and NS, and a refused change keeps the old record serving until the blocker is gone
• Eight planted defects each fail a test
• CI passes on this branch

Fixes #225