Remove support for Amazon Linux 2

[rifelpet]

AL2 reaches end of life in June. We've removed all kops e2e tests for it in kubernetes/test-infra#36344. We can remove support for it in kOps entirely.

This PR is targeting 1.35 but we can push it to 1.36 if desired.

/hold for feedback

[hakman]

Sounds good to me, no objection here.
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hakman

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [hakman]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.

[rifelpet]

/hold cancel

[justinsb]

I think the notice period is problematic for removal in 1.35. If AL2 no longer works because of things AWS did, then I think we could remove support. Otherwise I think we should probably remove in 1.36 (but I think it's fine to go beyond just deprecation, e.g. to say that "AL2 is EOL as of June 30 2026 and users are encouraged to move to AL2023. kOps is prioritizing AL2023 support over AL2 support." But given that EOL is June, I think removal in 1.36 feels right? WDYT?