cleanup: remove stale sig-release subproject hyperkube links

The hyperkube subproject linked OWNERS files 404 since hyperkube went
away a year ago.  Update to reflect the best-effort support of hyperkube
until 1.18 is EOL.

Signed-off-by: Tim Pepper <[email protected]>

Author: Tim Pepper

sig-release/README.md

@@ -78,10 +78,10 @@ Documents and processes related to SIG Release
 - **Owners:**
   - https://raw.githubusercontent.com/kubernetes/sig-release/master/OWNERS
 ### hyperkube
+Best-effort maintaining of hyperkube until 1.18 goes EOL 2021-04-30.
 - **Owners:**
-  - https://raw.githubusercontent.com/kubernetes/kubernetes/master/build/debian-hyperkube-base/OWNERS
-  - https://raw.githubusercontent.com/kubernetes/kubernetes/master/cluster/images/hyperkube/OWNERS
-  - https://raw.githubusercontent.com/kubernetes/kubernetes/master/cmd/hyperkube/OWNERS
+  - https://raw.githubusercontent.com/kubernetes/kubernetes/release-1.18/cluster/images/hyperkube/OWNERS
+  - https://raw.githubusercontent.com/kubernetes/release/master/images/build/debian-hyperkube-base/OWNERS
 ### kubernetes/repo-infra
 Creates and maintains tools and templates for Kubernetes org repositories.
 Includes bazel tooling for managing dependencies for kubernetes/kubernetes

sigs.yaml

@@ -1876,10 +1876,11 @@ sigs:
     owners:
     - https://raw.githubusercontent.com/kubernetes/sig-release/master/OWNERS
   - name: hyperkube
+    description: |
+      Best-effort maintaining of hyperkube until 1.18 goes EOL 2021-04-30.
     owners:
-    - https://raw.githubusercontent.com/kubernetes/kubernetes/master/build/debian-hyperkube-base/OWNERS
-    - https://raw.githubusercontent.com/kubernetes/kubernetes/master/cluster/images/hyperkube/OWNERS
-    - https://raw.githubusercontent.com/kubernetes/kubernetes/master/cmd/hyperkube/OWNERS
+    - https://raw.githubusercontent.com/kubernetes/kubernetes/release-1.18/cluster/images/hyperkube/OWNERS
+    - https://raw.githubusercontent.com/kubernetes/release/master/images/build/debian-hyperkube-base/OWNERS
   - name: kubernetes/repo-infra
     description: |
       Creates and maintains tools and templates for Kubernetes org repositories.