chore(ci): fix script path, remove unused (#3402)

Fixes the cleanup script path in the workflow definition and removes more unused code.

Author: czeslavo

.github/workflows/cleanup.yaml

@@ -29,7 +29,7 @@ jobs:
             ${{ runner.os }}-build-codegen-
 
       - name: cleanup orphaned test clusters
-        run: go run hack/e2e/cluster/cleanup/main.go all
+        run: go run hack/cleanup_gke_clusters.go
         env:
           GOOGLE_APPLICATION_CREDENTIALS: ${{ secrets.GOOGLE_APPLICATION_CREDENTIALS }}
           GOOGLE_PROJECT: ${{ secrets.GOOGLE_PROJECT }}