Remove eks_addon_vpccni_prefix_delegation_enabled var and make it enabled by default

[wcarlsen]

Describe your changes

VPC prefix delegation is enabled in all our shared clusters see https://github.com/dfds/eks-pipeline/blob/91b62ba71cef0136f8a434f38eb3a7115743aa2c/cluster.hcl#L9, but apparently still disabled by default here. So we remove the variable and enable the feature by default.

As a side effect max_pods default of 110 will always be set unless explicitly overwritten. This is in my mind a sane default and also what the Kubernetes team recommends. Plus this behavior was already present in our shared clusters.

Since this will cause a noderollover we swallow this #2056 in this one as well.

Issue ticket number and link

Checklist before requesting a review

• I have tested changes in my sandbox
• I have added the needed changes in the test/integration folder to apply my changes in QA. Read the guide on adding environment variables in QA
• I have rebased the code to master (or merged in the latest from master)

Is it a new release?

• Apply a release tag release:(major|minor|patch), following semantic versioning in this guide or norelease if there is no changes to the Terraform code

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