Remove skipped test for GCP credentials
Remove skipped test for GCP credentials

When the test cases for pod creation were written, there was an
assumption that GCP credentials would be manually managed. However, the
system now relies on workload identity for GKE. Workload identity allows
the Google Cloud Platform to automatically manage credentials on GKE
clusters. This commit removes the skipped, now-unnecessary test case.

grpc/test-infra,grpc/test-infra