cleanup: remove management and leftovers of cik8s and eks-public EKS clusters

[dduportal]

As per jenkins-infra/helpdesk#3954 (comment),

this PR removes the leftovers of these 2 clusters, namely:

• The 2 clusters, but also their networks and IAM resources
• The Terraform providers (and their associated updatecli manifests) only used by the removed resources
• The ci.jenkins.io S3 bucket resources as the artifacts are now archived on the VM (in Azure)

=> Note: this PR effectively cleans up the AWS resource management. Only leftovers are non functionnal for now, until we start using the new AWS account:

• The SSH public key for agents is used by jenkins-infra/packer-images and will have to be migrated to shared-tools later
• The other elements are locals or variables

[dduportal]

OK, removing all resources at once is failing the Terraform process 😄 . Let's split in different PRs

[dduportal]

This PR is expected to have no changes: all resources had to be deleted manually

[dduportal]

No changes. Your infrastructure matches the configuration.