When subnet is moved into a shared network the old subnet entry is not removed
I did the following test:
- Started Kea with a single subnet and without any shared networks
- I let Stork pull the subnet and store in its database
- Stopped Kea and moved the subnet into a new shared network
- Started Kea again and let Stork pull the updated configuration
- Navigated to the list of subnets
- I now see two instances of the same subnet, one under shared network and one global.