make extension-down: Delete the validating webhook of the admission component

[ialidzhikov]

How to categorize this PR?

/area dev-productivity /kind enhancement

What this PR does / why we need it: Locally, I hit the following issue. I executed make extension-down while I still had a Shoot with enabled registry-cache extension. The admission helm chart was deleted by make extension down which under the hood runs skaffold delete. But the admission webhook was still present in the system (not part of the chart) and was blocking updates of the Shoot because there was no admission Pod running anymore. After https://github.com/gardener/gardener-extension-registry-cache/pull/122 the validating webhook is no longer part of the admission chart but it is created on admission Pod startup. Hence, we have to delete it explicitly.

Which issue(s) this PR fixes: N/A

Special notes for your reviewer: N/A

Release note:

NONE

[ialidzhikov]

/hold Maybe the same has to be applied for make remote-extension-down. Let me check.

[gardener-prow[bot]]

LGTM label has been added.

Git tree hash: 9a523e93868653bd4e34cdc89956d8c7c912bcd0

[gardener-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dimitar-kostadinov

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[ialidzhikov]

/hold cancel