Remove proxy-kubeconfig.yaml.

I don't believe this is used by any tests or docs. I think it was for some initial local testing of the impersonation proxy?

Signed-off-by: Matt Moyer <moyerm@vmware.com>

proxy-kubeconfig.yaml

@@ -1,16 +0,0 @@
-apiVersion: v1
-clusters:
-  - cluster:
-      server: https://127.0.0.1:8444
-      insecure-skip-tls-verify: true
-    name: kind-pinniped
-contexts:
-  - context:
-      cluster: kind-pinniped
-      user: kind-pinniped
-    name: kind-pinniped
-current-context: kind-pinniped
-kind: Config
-preferences: {}
-users:
-  - name: kind-pinniped