Remove support for the deprecated auto-generated subnet IDs feature

It is one of the reasons why auto-generated subnet identifiers are deprecated starting from Kea version 2.4.0.

The deprecation happened in Kea 2.4. Kea 2.4 shipped with the deprecation warning in the ARM. Kea 2.5 can have the feature removed.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information