Compilation error on HEAD: Add JSONBase to v1beta3/types.go to prevent it

On a clean checkout (at https://github.com/GoogleCloudPlatform/kubernetes/commit/fd5a9080707fa871fb8b46d161816f84eb675b31), when I do `go build`, I get a compilation error:

```
sghods-mba:kubernetes sam$ go build ./...
# github.com/GoogleCloudPlatform/kubernetes/pkg/api/v1beta3
pkg/api/v1beta3/types.go:839: undefined: JSONBase
```

I'm sure the intent was to fully remove JSONBase, but I don't know how to do that, so I did the minimal amount to just fix the build.