vc-syncer: remove invalid cluster name from knownClusterSet

[crazywill]

What this PR does / why we need it: bugfix: remove invalid cluster name from knownClusterSet

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

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[k8s-ci-robot]

Hi @crazywill. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[christopherhein]

/ok-to-test

[christopherhein]

@Fei-Guo can you verify what this might do? I'm not as familiar these days w/ how the knownClusterSet works.

[Fei-Guo]

The checkers in other controllers have already been fixed with "Delete". This change seems to fix the missing piece.

/approve /lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: crazywill, Fei-Guo

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Needs approval from an approver in each of these files: - ~~[virtualcluster/OWNERS](https://github.com/kubernetes-sigs/cluster-api-provider-nested/blob/main/virtualcluster/OWNERS)~~ [Fei-Guo] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment