skaffold: Remove custom tagPolicy for the admission

[ialidzhikov]

How to categorize this PR?

/area dev-productivity
/kind cleanup

What this PR does / why we need it:
In gardener/gardener-extension-shoot-rsyslog-relp#194 (comment) @plkokanov found that we don't need a custom tagPolicy for the admission.

Which issue(s) this PR fixes:
Follow-up after #279

Special notes for your reviewer:
N/A

Release note:

NONE

[dimitar-kostadinov]

/lgtm

[gardener-prow]

LGTM label has been added.

Git tree hash: 92634ba013a0aa87adbd82c4e2d2a9aba7838cd0

[dimitar-kostadinov]

Root pod creation failed:

  [FAILED] Unexpected error:
      <*errors.joinError | 0xc000150198>: 
      error sending request: Post "https://api.e2e-cache-pr.local.external.local.gardener.cloud/api/v1/namespaces/kube-system/pods/rootpod-865/exec?command=%2Fbin%2Fsh&container=root-container&stderr=true&stdin=true&stdout=true&tty=false": read tcp 172.18.255.1:47188->172.18.255.1:443: read: connection reset by peer
      {
          errs: [
              <*errors.errorString | 0xc00012c100>{
                  s: "error sending request: Post \"https://api.e2e-cache-pr.local.external.local.gardener.cloud/api/v1/namespaces/kube-system/pods/rootpod-865/exec?command=%2Fbin%2Fsh&container=root-container&stderr=true&stdin=true&stdout=true&tty=false\": read tcp 172.18.255.1:47188->172.18.255.1:443: read: connection reset by peer",
              },
          ],
      }
  occurred

/test pull-gardener-extension-registry-cache-e2e-kind

[ialidzhikov]

/approve

[gardener-prow]

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