Remove test jobs for alpha.kubernetes.io/nvidia-gpu.
Remove test jobs for alpha.kubernetes.io/nvidia-gpu.

Support for it was removed in kubernetes/kubernetes#61498

GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid