Cleanup: remove in-tree cloud provider support

[tico88612]

What type of PR is this?

/kind cleanup /kind documentation

What this PR does / why we need it:

Kubernetes v1.31 remove in-tree cloud provider related code, we should remove related support.

Which issue(s) this PR fixes:

Fixes #10495

Special notes for your reviewer:

Waiting for #11378 get merge.

Does this PR introduce a user-facing change?:

[action required] no longer support in-tree cloud provider, please delete or write `external` to the `cloud_provider` variable.

[k8s-ci-robot]

Skipping CI for Draft Pull Request. If you want CI signal for your change, please convert it to an actual PR. You can still manually trigger a test run with /test all

[VannTen]

I don't actually think we need to wait for #11378 : since kubernetes v1.31 does not support in-tree provider, even if kubespray has support, it won't work. So let's proceed with the removal :+1:

[tico88612]

/label tide/merge-method-merge /ok-to-test

[VannTen]

/approve Thanks for the work !

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MrFreezeex, tico88612, VannTen

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