Drop the pool-less 198.18.25.0/24 subnet from the migration samples

The 'local' subnet is not needed in the kea migration. Remove it from the ISC
translation sample; the pool-less-subnet capability and its unit tests remain.

- remove net-198-18-25 KeaSubnet from config/samples/01-subnets.yaml

Claude-Session: https://claude.ai/code/session_01JUoARVdmhxKQHyyyp1pxeT

config/samples/01-subnets.yaml

@@ -1,6 +1,5 @@
-# Full translation of the legacy ISC dhcpd pools: 198.18.13-17.0/24 each with a
+# Translation of the legacy ISC dhcpd pools: 198.18.13-17.0/24 each with a
-# .200-.220 pool, plus 198.18.25.0/24 with no pool (declared so relayed requests
+# .200-.220 pool. routers .1, dns 198.18.19.15, next-server 198.18.19.19.
-# are still serviced). routers .1, dns 198.18.19.15, next-server 198.18.19.19.
 apiVersion: kea.unkin.net/v1alpha1
 kind: KeaSubnet
 metadata:
@@ -75,17 +74,3 @@ spec:
   dnsServers: [198.18.19.15]
   domainName: main.unkin.net
   nextServer: 198.18.19.19
----
-# No pool: declared so relayed DHCP requests on this net are matched and get
-# options, but no dynamic address is allocated (subnet-mask derives from CIDR).
-apiVersion: kea.unkin.net/v1alpha1
-kind: KeaSubnet
-metadata:
-  name: net-198-18-25
-  namespace: dhcp-system
-spec:
-  clusterRef: pxe
-  subnet: 198.18.25.0/24
-  routers: [198.18.25.1]
-  dnsServers: [198.18.19.15]
-  domainName: main.unkin.net