Description of problem:
Before we started using Jinja to dynamically create NIC config templates, it was necessary to have a separate template for controllers using IPv6. The controller-v6.yaml templates in each of the directories in network/config/* would have an IPv6 default route on the External network and an IPv4 default route on the Control Plane. Now that we generate NIC configs with Jinja, it is only necessary to put both networks in the role config, so these legacy templates are no longer required.

When we started generating these templates with Jinja, we also updated controller-v6.yaml to be generated with Jinja. The original purpose of keeping the controller-v6.yaml templates even after implementing Jinja was to support upgrades. However, it is unlikely that we would find operators using the built-in templates in production, and we can document the new filename in upgrade documentation.

Version-Release number of selected component (if applicable):
Stein/OSP 15

Actual results:
The controller-v6.yaml templates still exist, so that someone upgrading from a previous deployment that uses that template will not have to update their environment files to point to a different file. However, this file is not needed if the user changes to point to controller.yaml instead of controller-v6.yaml in their environment files.

Expected results:
Since we are generating configs with Jinja now, and the controller-v6.yaml is no longer required, it makes sense to require users to use the generated controller.yaml file instead. This will also ensure that the latest features (such as automatic host route inclusion for routed spine/leaf) will be available.

Additional info:
Removing these files will require operators to update which NIC config to use if they are upgrading an IPv6 environment. However, it is unlikely that anyone is using the included controller-v6.yaml without modifications. If the user is using a custom version of this file, they can continue to use that same file.