Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

discovery client not depend on pkg/api/legacyscheme

Switch kubectl's cached discovery client to use kubect's scheme (pkg/kubectl/scheme) which only registered with external version types.

The encoding and decoding here uses only `k8s.io/apimachinery/pkg/apis/meta/v1.APIGroupList` and `k8s.io/apimachinery/pkg/apis/meta/v1.APIResourceList` which are not internal version. So it should be safe.

```release-note
NONE
```

/assign @monopole