github: Remove unused files

Signed-off-by: Michi Mutsuzaki <[email protected]>

Author: michi-covalent

Diff for: .github/get-kubeconfig.sh

@@ -15,7 +15,6 @@
 /RELEASE.md @cilium/cilium-cli-maintainers
 /.github/ @cilium/contributing
 /.github/gcp-vm-startup.sh @cilium/ci-structure
-/.github/get-kubeconfig.sh @cilium/github-sec @cilium/ci-structure
 /.github/kind-config*.yaml @cilium/ci-structure
 /.github/tools/ @cilium/ci-structure
 /.github/workflows/ @cilium/github-sec @cilium/ci-structure