Delete in-tree support for NVIDIA GPUs.

This removes the alpha Accelerators feature gate which was deprecated in 1.10.
The alternative feature DevicePlugins went beta in 1.10.

pkg/apis/core/helper/helpers_test.go

@@ -387,10 +387,6 @@ func TestIsOvercommitAllowed(t *testing.T) {
 			name:    core.ResourceMemory,
 			allowed: true,
 		},
-		{
-			name:    core.ResourceNvidiaGPU,
-			allowed: false,
-		},
 		{
 			name:    HugePageResourceName(resource.MustParse("2Mi")),
 			allowed: false,