operator: drop REST API workaround for SEV-SNP GCP instances

[msanft]

Context

Previously, we couldn't just rely on our copy-based approach to generate instance templates for target instance groups on GCP SEV-SNP upgrades, as their client library didn't expose the confidential_instance_type field that specifies whether an SEV or SEV-SNP VM should be created. We always received SEV VMs, as this was the default. Obviously, this broke SEV-SNP upgrades. Now, they've incorporated the field in v1.29.0 of their client library, which we're already on, so we can just drop the workaround commit.

This reverts commit effb086.

Related Issue: googleapis/google-cloud-go#10873

Proposed change(s)

• Revert the workaround commit, going back to the non-REST approach.

Additional info

• AB#4988

Checklist

• Run the E2E tests that are relevant to this PR's changes
  • GCP SEV-SNP upgrade
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?
• Link to Milestone

[netlify]

✅ Deploy Preview for constellation-docs canceled.

Name	Link
🔨 Latest commit	b816af5
🔍 Latest deploy log	https://app.netlify.com/sites/constellation-docs/deploys/67597c62e951f400084b941a

[github-actions]

Coverage report

Package	Old	New	Trend
operators/constellation-node-operator/internal/cloud/gcp/client	80.20%	80.30%	↗️