Remove "design docs" from /docs/reference sidebar (#6410)

This list on the sidebar isn't very useful:

- it's not an exhaustive list
- it's not an up-to-date list either
- design docs are not documentation (they're already stale)
- we already link to the full list from https://kubernetes.io/docs/reference/
  home page

Also removing the 'docs/admin/ovs-networking.md' document as per
the pull request comments, it's no longer necessary.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

_data/reference.yml

@@ -103,22 +103,6 @@ toc:
   - docs/reference/generated/federation-apiserver.md
   - docs/reference/generated/federation-controller-manager.md
 
-- title: Kubernetes Design Docs
-  landing_page: /docs/reference/design-docs/overview/
-  section:
-  - docs/reference/design-docs/overview.md
-  - title: Kubernetes Architecture
-    path: https://git.k8s.io/community/contributors/design-proposals/architecture/architecture.md
-  - title: Kubernetes Design Overview
-    path: https://github.com/kubernetes/kubernetes/tree/release-1.6/docs/design
-  - title: Kubernetes Identity and Access Management
-    path: https://git.k8s.io/community/contributors/design-proposals/auth/access.md
-  - docs/admin/ovs-networking.md
-  - title: Security Contexts
-    path: https://git.k8s.io/community/contributors/design-proposals/auth/security_context.md
-  - title: Security in Kubernetes
-    path: https://git.k8s.io/community/contributors/design-proposals/auth/security.md
-
 - title: Kubernetes Issues and Security
   landing_page: https://github.com/kubernetes/kubernetes/issues/
   section: