Allow adding remote network config to private clusters

[NicholasBlaskey]

Description

Remove validation rules that prevented remote network config from being used with private clusters.

Tested manually that validation did not fail with privateCluster.enabled=true added to this file https://github.com/eksctl-io/eksctl/blob/main/examples/43-hybrid-nodes.yaml

Checklist

• Added tests that cover your change (if possible)
• [none required] Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[github-actions]

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